{"id":5402,"date":"2026-10-23T20:51:20","date_gmt":"2026-10-23T12:51:20","guid":{"rendered":"https:\/\/ballvalves.tw\/?p=5402"},"modified":"2026-10-23T21:04:14","modified_gmt":"2026-10-23T13:04:14","slug":"pipe-thread-chart","status":"publish","type":"post","link":"https:\/\/ballvalves.tw\/fr\/pipe-thread-chart\/","title":{"rendered":"Pipe Thread Chart: NPT, BSPT and BSPP Thread Dimensions, 1\/8\u2033 to 6\u2033"},"content":{"rendered":"
\n

Short answer:<\/strong> NPT, BSPT and BSPP share nominal sizes but do not seal against each other. NPT (ASME B1.20.1) is a 60\u00b0 taper thread. BSPT (R and Rc in ISO 7-1 and JIS B 0203; PT in Taiwan and Japan) is a 55\u00b0 taper thread. BSPP (G; PF in JIS) is a 55\u00b0 parallel thread that seals on a washer, not on the thread. The chart below gives pitch, thread height, engagement lengths and diameters in millimeters, 1\/8\u2033 to 6\u2033.<\/p>\n<\/div>\n\n\n\n

This pipe thread chart covers the three threads found on stainless steel valves and threaded fittings, NPT, BSPT and BSPP, in every nominal size from 1\/8\u2033 to 6\u2033. All values are in millimeters, with the NPT engagement lengths and the NPS pipe diameters also given in inches. Wherever the standards give basic dimensions, the values were recalculated from ASME B1.20.1 and JIS B 0203 rather than copied from an older catalog, and the cells where no second source could be found are left blank instead of filled in.<\/p>\n\n\n\n

Before ordering a threaded valve from another country, check whether its 1\/2\u2033 thread is the same as the one in your plant. Sometimes it is. Often it is not, and the difference only shows once the line is pressurized.<\/p>\n\n\n\n

Pipe thread chart: quick reference, 1\/8\u2033 to 6\u2033<\/h2>\n\n\n\n

Table 1 gives threads per inch, pitch, thread height and pipe outside diameter for NPT and for BSPT and BSPP at every nominal size, with a column that marks where the pitches coincide. It answers the two questions that come first: which size is this thread, and is it NPT or BSP. The pipe diameters are NPS (Nominal Pipe Size) steel pipe for NPT and JIS G 3452 steel pipe for BSPT. The sheet below carries the same data together with the thread form diagrams; Tables 3 to 7 further down give the full engagement lengths and diameters.<\/p>\n\n\n\n

\"Pipe
The pipe thread reference sheet: thread form diagrams for NPT, BSPT and BSPP, and the full dimension table from 1\/8\u2033 to 6\u2033.<\/figcaption><\/figure>\n\n\n\n

Table 1. Thread form and pipe outside diameter by size<\/h3>\n\n\n\n
\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Taille<\/th>\nNPT n<\/th>\nNPT p (mm)<\/th>\nNPT h (mm)<\/th>\nBSPT \/ BSPP n<\/th>\nBSPT \/ BSPP p (mm)<\/th>\nBSPT \/ BSPP h (mm)<\/th>\nSame pitch?<\/th>\nPipe OD, NPS (in)<\/th>\nPipe OD, NPS (mm)<\/th>\nPipe OD, JIS G 3452 (mm)<\/th>\n<\/tr>\n<\/thead>\n
1\/8\u2033<\/th>\n27<\/td>\n0.941<\/td>\n0.753<\/td>\n28<\/td>\n0.907<\/td>\n0.581<\/td>\nNon<\/td>\n0.405<\/td>\n10.3<\/td>\n10.5<\/td>\n<\/tr>\n
1\/4\u2033<\/th>\n18<\/td>\n1.411<\/td>\n1.129<\/td>\n19<\/td>\n1.337<\/td>\n0.856<\/td>\nNon<\/td>\n0.540<\/td>\n13.7<\/td>\n13.8<\/td>\n<\/tr>\n
3\/8\u2033<\/th>\n18<\/td>\n1.411<\/td>\n1.129<\/td>\n19<\/td>\n1.337<\/td>\n0.856<\/td>\nNon<\/td>\n0.675<\/td>\n17.1<\/td>\n17.3<\/td>\n<\/tr>\n
1\/2\u2033<\/th>\n14<\/td>\n1.814<\/td>\n1.451<\/td>\n14<\/td>\n1.814<\/td>\n1.162<\/td>\nOui<\/td>\n0.840<\/td>\n21.3<\/td>\n21.7<\/td>\n<\/tr>\n
3\/4\u2033<\/th>\n14<\/td>\n1.814<\/td>\n1.451<\/td>\n14<\/td>\n1.814<\/td>\n1.162<\/td>\nOui<\/td>\n1.050<\/td>\n26.7<\/td>\n27.2<\/td>\n<\/tr>\n
1\u2033<\/th>\n11.5<\/td>\n2.209<\/td>\n1.767<\/td>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\nNon<\/td>\n1.315<\/td>\n33.4<\/td>\n34.0<\/td>\n<\/tr>\n
1-1\/4\u2033<\/th>\n11.5<\/td>\n2.209<\/td>\n1.767<\/td>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\nNon<\/td>\n1.660<\/td>\n42.2<\/td>\n42.7<\/td>\n<\/tr>\n
1-1\/2\u2033<\/th>\n11.5<\/td>\n2.209<\/td>\n1.767<\/td>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\nNon<\/td>\n1.900<\/td>\n48.3<\/td>\n48.6<\/td>\n<\/tr>\n
2\u2033<\/th>\n11.5<\/td>\n2.209<\/td>\n1.767<\/td>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\nNon<\/td>\n2.375<\/td>\n60.3<\/td>\n60.5<\/td>\n<\/tr>\n
2-1\/2\u2033<\/th>\n8<\/td>\n3.175<\/td>\n2.540<\/td>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\nNon<\/td>\n2.875<\/td>\n73.0<\/td>\n76.3<\/td>\n<\/tr>\n
3\u2033<\/th>\n8<\/td>\n3.175<\/td>\n2.540<\/td>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\nNon<\/td>\n3.500<\/td>\n88.9<\/td>\n89.1<\/td>\n<\/tr>\n
4\u2033<\/th>\n8<\/td>\n3.175<\/td>\n2.540<\/td>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\nNon<\/td>\n4.500<\/td>\n114.3<\/td>\n114.3<\/td>\n<\/tr>\n
5\u2033<\/th>\n8<\/td>\n3.175<\/td>\n2.540<\/td>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\nNon<\/td>\n5.563<\/td>\n141.3<\/td>\n139.8<\/td>\n<\/tr>\n
6\u2033<\/th>\n8<\/td>\n3.175<\/td>\n2.540<\/td>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\nNon<\/td>\n6.625<\/td>\n168.3<\/td>\n165.2<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n\n\n

Look at the pitch columns before anything else. NPT and BSP threads (BSPT and BSPP have the same pitch at every size) coincide only at 1\/2\u2033 and 3\/4\u2033, where both families have 14 threads per inch. At 1\/8\u2033, 1\/4\u2033 and 3\/8\u2033 they differ by one thread per inch, from 1\u2033 to 2\u2033 by half a thread, and from 2-1\/2\u2033 up NPT drops to 8 threads per inch while BSP stays at 11. That pattern decides which mismatches screw together and which do not, and it comes up again below.<\/p>\n\n\n\n

NPT, BSPT and BSPP: what each pipe thread is<\/h2>\n\n\n\n

NPT is the American taper pipe thread of ASME B1.20.1: a 60\u00b0 thread angle, a taper of 1 in 16 on diameter, and a joint that seals on the thread itself. BSPT is the British Standard taper pipe thread, defined internationally in ISO 7-1 and in Japan in JIS B 0203: a 55\u00b0 thread angle, the same 1 in 16 taper, also sealing on the thread. BSPP is the British Standard parallel pipe thread of ISO 228-1 and JIS B 0202: 55\u00b0, no taper, and a joint that must be sealed on a face by a washer, O-ring or bonded seal, because the thread cannot seal by itself.<\/p>\n\n\n\n

The three are easiest to keep apart by their designations, because the designation is what appears on a drawing or an RFQ (request for quotation).<\/p>\n\n\n\n

NPT<\/strong> is written as nominal size, threads per inch and the letters NPT, for example 1\/2-14 NPT. The thread height is 0.8 times the pitch, and both the external and the internal thread are tapered. The ASME B1.20.1 standard<\/a> defines it together with the straight pipe threads NPSC, NPSM and NPSL (for couplings, mechanical joints and locknuts) of the same family.<\/p>\n\n\n\n

BSPT<\/strong> appears under several names that all mean the same thread. ISO 7-1<\/a> writes the external taper thread R and the internal taper thread Rc, and it also defines Rp, an internal parallel thread made to assemble with an R external thread. JIS B 0203 uses the same letters and keeps the older symbol PT in an appendix, so PT 1\/2 on a Taiwanese or Japanese drawing is the same thread as R 1\/2 or Rc 1\/2. The thread height is 0.640327 times the pitch, and the crest and root are rounded.<\/p>\n\n\n\n

BSPP<\/strong> is written G in ISO 228-1 and JIS B 0202, and PF in the older JIS notation. At each nominal size it has the same 55\u00b0 form and the same pitch as BSPT, but no taper. The scope of ISO 228-1<\/a> states that the threads are for the mechanical assembly of fittings, valves and accessories, and that a pressure-tight joint is made by compressing two surfaces outside the thread with a seal between them. External G threads are made to tolerance class A or B.<\/p>\n\n\n\n

Table 2. NPT, BSPT and BSPP side by side<\/h3>\n\n\n\n
\n\n\n\n\n\n\n\n\n\n\n\n\n
<\/th>\nNPT<\/th>\nBSPT<\/th>\nBSPP<\/th>\n<\/tr>\n<\/thead>\n
Standard<\/th>\nASME B1.20.1<\/td>\nISO 7-1; JIS B 0203<\/td>\nISO 228-1; JIS B 0202<\/td>\n<\/tr>\n
D\u00e9signation<\/th>\nNPT (e.g. 1\/2-14 NPT)<\/td>\nR external, Rc internal taper, Rp internal parallel; PT in older JIS<\/td>\nG (external class A or B); PF in older JIS<\/td>\n<\/tr>\n
Thread angle<\/th>\n60\u00b0<\/td>\n55\u00b0<\/td>\n55\u00b0<\/td>\n<\/tr>\n
Taper<\/th>\n1 in 16 on diameter<\/td>\n1 in 16 on diameter<\/td>\nNone (parallel)<\/td>\n<\/tr>\n
Thread height<\/th>\n0.8 p<\/td>\n0.640327 p, rounded crest and root<\/td>\n0.640327 p, rounded crest and root<\/td>\n<\/tr>\n
Where the joint seals<\/th>\nOn the thread, with sealant<\/td>\nOn the thread, with sealant<\/td>\nOn a face outside the thread: washer, O-ring or bonded seal<\/td>\n<\/tr>\n
Mates with<\/th>\nNPT internal thread<\/td>\nRc or Rp internal thread<\/td>\nG internal thread<\/td>\n<\/tr>\n
Common in<\/th>\nUnited States, Canada<\/td>\nUnited Kingdom, Europe, Japan, Taiwan, much of Asia<\/td>\nSame regions as BSPT, where the joint has a sealing face<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n\n\n

How to read the detailed tables<\/h2>\n\n\n\n

Tables 3 to 6 give, for every nominal size, the engagement lengths on the external and internal thread (a, a + f, \u2113, \u2113\u2032 and t) and the diameters at the points those lengths define (\u00d8D0 to \u00d8D4). The diameters are measured at or from the gauge plane, the reference cross-section where the basic diameters of a taper thread apply: at the hand-tight engagement L1 from the pipe end on NPT, and at the basic gauge length a on BSPT. Lengths are also given as a number of threads, because that is how a fitter counts turns. The diagram on the sheet above shows where each symbol sits on a male and a female thread.<\/p>\n\n\n\n

The symbols follow the sheet. Where a value comes straight from a standard, the standard is named; where it is calculated from the standard’s basic dimensions, the formula is given, so any cell can be checked.<\/p>\n\n\n\n

Column key<\/h3>\n\n\n\n
\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Symbol<\/th>\nMeaning<\/th>\nNPT<\/th>\nBSPT<\/th>\n<\/tr>\n<\/thead>\n
n<\/th>\nThreads per inch (threads in 25.4 mm)<\/td>\nASME B1.20.1<\/td>\nJIS B 0203<\/td>\n<\/tr>\n
p<\/th>\nPitch, 25.4 \u00f7 n<\/td>\nCalculated<\/td>\nCalculated<\/td>\n<\/tr>\n
h<\/th>\nThread height<\/td>\n0.8 p<\/td>\n0.640327 p<\/td>\n<\/tr>\n
a<\/th>\nHand-tight engagement of the external thread, from the pipe end<\/td>\nL1<\/td>\nBasic gauge length a, pipe end to gauge plane<\/td>\n<\/tr>\n
a + f<\/th>\nUseful external thread length, from the pipe end<\/td>\nL2, effective thread length<\/td>\na plus f, the minimum useful thread beyond the gauge plane<\/td>\n<\/tr>\n
\u2113<\/th>\nMake-up length (NPT); useful internal taper thread length (BSPT)<\/td>\nL1 + L3; L3 is the wrench make-up allowance, 3 threads up to 2\u2033 and 2 threads from 2-1\/2\u2033<\/td>\nMinimum useful length of the internal taper thread (Rc), from the gauge plane<\/td>\n<\/tr>\n
\u2113\u2032<\/th>\nMinimum useful length of a parallel internal thread (Rp), from the fitting face, allowing for incomplete threads<\/td>\nNot defined<\/td>\nJIS B 0203<\/td>\n<\/tr>\n
t<\/th>\nMinimum internal thread length with no incomplete threads<\/td>\nClass 150 fitting minimum thread length, ASME B16.3<\/td>\nJIS B 0203<\/td>\n<\/tr>\n
\u00d8D1<\/th>\nMinor diameter at the gauge plane<\/td>\nE1 \u2212 h (E1 is the pitch diameter at the hand-tight plane)<\/td>\nd1<\/td>\n<\/tr>\n
\u00d8D3<\/th>\nMinor diameter at depth t into the internal thread<\/td>\n\u00d8D1 \u2212 t \u00f7 16<\/td>\n\u00d8D1 \u2212 t \u00f7 16<\/td>\n<\/tr>\n
\u00d8D4<\/th>\nMinor diameter at depth \u2113 into the internal thread<\/td>\n\u00d8D1 \u2212 \u2113 \u00f7 16<\/td>\n\u00d8D1 \u2212 \u2113 \u00f7 16<\/td>\n<\/tr>\n
\u00d8D0<\/th>\nMajor diameter at the pipe end (small end of the external thread)<\/td>\nE0 + h (E0 is the pitch diameter at the pipe end)<\/td>\nd \u2212 a \u00f7 16 (d is the major diameter at the gauge plane)<\/td>\n<\/tr>\n
\u00d8D2<\/th>\nMajor diameter at the end of the useful external thread<\/td>\n\u00d8D0 + L2 \u00f7 16<\/td>\nd + f \u00f7 16<\/td>\n<\/tr>\n
OD<\/th>\nOutside diameter of the pipe the thread is cut on<\/td>\nNPS (Nominal Pipe Size) steel pipe, ASME B36.10M<\/td>\nSGP (carbon steel pipe for ordinary piping), JIS G 3452<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n\n\n

Two notes on the internal thread columns. ASME B1.20.1 sets the thread dimensions and the make-up allowance L3, but not a minimum length of complete thread in a fitting, so the NPT t column uses the Class 150 minimum thread length of ASME B16.3<\/a> (Class 150 is one of the two pressure classes of threaded fittings in that standard), as listed by a fitting maker and a stainless fitting distributor. No second source was found for 5\u2033 and 6\u2033, so those two cells are blank. ISO 228-1 and JIS B 0202 set no thread length for G; the \u2113\u2032 and t values in Table 5 are for Rp, and the sheet above uses them as the female lengths for a parallel thread.<\/p>\n\n\n\n

NPT and BSPT thread dimensions, 1\/8\u2033 to 6\u2033<\/h2>\n\n\n\n

Tables 3 and 4 are NPT, Tables 5 and 6 are BSPT, and Table 7 is BSPP. Everything is in millimeters except the columns marked (in), and threads per inch is the count over 25.4 mm. The inch values in Table 3 are the ASME B1.20.1 basic dimensions; the millimeter columns convert them at 25.4 mm per inch.<\/p>\n\n\n\n

Table 3. NPT engagement lengths, ASME B1.20.1<\/h3>\n\n\n\n
\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Taille<\/th>\nn<\/th>\na = L1 (mm)<\/th>\nL1 (in)<\/th>\na in threads<\/th>\na + f = L2 (mm)<\/th>\nL2 (in)<\/th>\n\u2113 = L1 + L3 (mm)<\/th>\nt, B16.3 min. (mm)<\/th>\nt in threads<\/th>\n<\/tr>\n<\/thead>\n
1\/8\u2033<\/th>\n27<\/td>\n4.102<\/td>\n0.1615<\/td>\n4.36<\/td>\n6.70<\/td>\n0.2639<\/td>\n6.92<\/td>\n6.35<\/td>\n6.75<\/td>\n<\/tr>\n
1\/4\u2033<\/th>\n18<\/td>\n5.786<\/td>\n0.2278<\/td>\n4.10<\/td>\n10.21<\/td>\n0.4018<\/td>\n10.02<\/td>\n8.13<\/td>\n5.76<\/td>\n<\/tr>\n
3\/8\u2033<\/th>\n18<\/td>\n6.096<\/td>\n0.240<\/td>\n4.32<\/td>\n10.36<\/td>\n0.4078<\/td>\n10.33<\/td>\n9.14<\/td>\n6.48<\/td>\n<\/tr>\n
1\/2\u2033<\/th>\n14<\/td>\n8.128<\/td>\n0.320<\/td>\n4.48<\/td>\n13.56<\/td>\n0.5337<\/td>\n13.57<\/td>\n10.92<\/td>\n6.02<\/td>\n<\/tr>\n
3\/4\u2033<\/th>\n14<\/td>\n8.611<\/td>\n0.339<\/td>\n4.75<\/td>\n13.86<\/td>\n0.5457<\/td>\n14.05<\/td>\n12.70<\/td>\n7.00<\/td>\n<\/tr>\n
1\u2033<\/th>\n11.5<\/td>\n10.160<\/td>\n0.400<\/td>\n4.60<\/td>\n17.34<\/td>\n0.6828<\/td>\n16.79<\/td>\n14.73<\/td>\n6.67<\/td>\n<\/tr>\n
1-1\/4\u2033<\/th>\n11.5<\/td>\n10.668<\/td>\n0.420<\/td>\n4.83<\/td>\n17.95<\/td>\n0.7068<\/td>\n17.29<\/td>\n17.02<\/td>\n7.71<\/td>\n<\/tr>\n
1-1\/2\u2033<\/th>\n11.5<\/td>\n10.668<\/td>\n0.420<\/td>\n4.83<\/td>\n18.38<\/td>\n0.7235<\/td>\n17.29<\/td>\n17.78<\/td>\n8.05<\/td>\n<\/tr>\n
2\u2033<\/th>\n11.5<\/td>\n11.074<\/td>\n0.436<\/td>\n5.01<\/td>\n19.22<\/td>\n0.7565<\/td>\n17.70<\/td>\n19.05<\/td>\n8.63<\/td>\n<\/tr>\n
2-1\/2\u2033<\/th>\n8<\/td>\n17.323<\/td>\n0.682<\/td>\n5.46<\/td>\n28.89<\/td>\n1.1375<\/td>\n23.67<\/td>\n23.37<\/td>\n7.36<\/td>\n<\/tr>\n
3\u2033<\/th>\n8<\/td>\n19.456<\/td>\n0.766<\/td>\n6.13<\/td>\n30.48<\/td>\n1.2000<\/td>\n25.81<\/td>\n24.89<\/td>\n7.84<\/td>\n<\/tr>\n
4\u2033<\/th>\n8<\/td>\n21.438<\/td>\n0.844<\/td>\n6.75<\/td>\n33.02<\/td>\n1.3000<\/td>\n27.79<\/td>\n27.43<\/td>\n8.64<\/td>\n<\/tr>\n
5\u2033<\/th>\n8<\/td>\n23.800<\/td>\n0.937<\/td>\n7.50<\/td>\n35.72<\/td>\n1.4063<\/td>\n30.15<\/td>\n\u2014<\/td>\n\u2014<\/td>\n<\/tr>\n
6\u2033<\/th>\n8<\/td>\n24.333<\/td>\n0.958<\/td>\n7.66<\/td>\n38.42<\/td>\n1.5125<\/td>\n30.68<\/td>\n\u2014<\/td>\n\u2014<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n\n\n

Table 4. NPT thread diameters (mm)<\/h3>\n\n\n\n
\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Taille<\/th>\nPipe OD<\/th>\n\u00d8D0 (pipe end)<\/th>\n\u00d8D2 (end of a + f)<\/th>\n\u00d8D1 (gauge plane)<\/th>\n\u00d8D3 (at t)<\/th>\n\u00d8D4 (at \u2113)<\/th>\n<\/tr>\n<\/thead>\n
1\/8\u2033<\/th>\n10.3<\/td>\n9.99<\/td>\n10.40<\/td>\n8.74<\/td>\n8.34<\/td>\n8.30<\/td>\n<\/tr>\n
1\/4\u2033<\/th>\n13.7<\/td>\n13.25<\/td>\n13.89<\/td>\n11.36<\/td>\n10.85<\/td>\n10.73<\/td>\n<\/tr>\n
3\/8\u2033<\/th>\n17.1<\/td>\n16.67<\/td>\n17.32<\/td>\n14.80<\/td>\n14.23<\/td>\n14.15<\/td>\n<\/tr>\n
1\/2\u2033<\/th>\n21.3<\/td>\n20.72<\/td>\n21.56<\/td>\n18.32<\/td>\n17.64<\/td>\n17.47<\/td>\n<\/tr>\n
3\/4\u2033<\/th>\n26.7<\/td>\n26.03<\/td>\n26.90<\/td>\n23.67<\/td>\n22.87<\/td>\n22.79<\/td>\n<\/tr>\n
1\u2033<\/th>\n33.4<\/td>\n32.59<\/td>\n33.68<\/td>\n29.69<\/td>\n28.77<\/td>\n28.65<\/td>\n<\/tr>\n
1-1\/4\u2033<\/th>\n42.2<\/td>\n41.32<\/td>\n42.44<\/td>\n38.45<\/td>\n37.39<\/td>\n37.37<\/td>\n<\/tr>\n
1-1\/2\u2033<\/th>\n48.3<\/td>\n47.39<\/td>\n48.54<\/td>\n44.52<\/td>\n43.41<\/td>\n43.44<\/td>\n<\/tr>\n
2\u2033<\/th>\n60.3<\/td>\n59.40<\/td>\n60.60<\/td>\n56.56<\/td>\n55.37<\/td>\n55.45<\/td>\n<\/tr>\n
2-1\/2\u2033<\/th>\n73.0<\/td>\n71.62<\/td>\n73.42<\/td>\n67.62<\/td>\n66.16<\/td>\n66.14<\/td>\n<\/tr>\n
3\u2033<\/th>\n88.9<\/td>\n87.39<\/td>\n89.30<\/td>\n83.53<\/td>\n81.97<\/td>\n81.92<\/td>\n<\/tr>\n
4\u2033<\/th>\n114.3<\/td>\n112.63<\/td>\n114.70<\/td>\n108.89<\/td>\n107.18<\/td>\n107.16<\/td>\n<\/tr>\n
5\u2033<\/th>\n141.3<\/td>\n139.46<\/td>\n141.70<\/td>\n135.87<\/td>\n\u2014<\/td>\n133.99<\/td>\n<\/tr>\n
6\u2033<\/th>\n168.3<\/td>\n166.27<\/td>\n168.67<\/td>\n162.71<\/td>\n\u2014<\/td>\n160.79<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n\n\n

Table 5. BSPT (R, Rc, PT) engagement lengths, JIS B 0203 (mm)<\/h3>\n\n\n\n
\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Taille<\/th>\nn<\/th>\na (gauge length)<\/th>\na in threads<\/th>\na + f<\/th>\n\u2113 (Rc, min.)<\/th>\n\u2113\u2032 (Rp, min.)<\/th>\nt (min.)<\/th>\nt in threads<\/th>\n<\/tr>\n<\/thead>\n
1\/8\u2033<\/th>\n28<\/td>\n3.97<\/td>\n4.38<\/td>\n6.47<\/td>\n6.20<\/td>\n7.40<\/td>\n4.40<\/td>\n4.85<\/td>\n<\/tr>\n
1\/4\u2033<\/th>\n19<\/td>\n6.01<\/td>\n4.50<\/td>\n9.71<\/td>\n9.40<\/td>\n11.00<\/td>\n6.70<\/td>\n5.01<\/td>\n<\/tr>\n
3\/8\u2033<\/th>\n19<\/td>\n6.35<\/td>\n4.75<\/td>\n10.05<\/td>\n9.70<\/td>\n11.40<\/td>\n7.00<\/td>\n5.24<\/td>\n<\/tr>\n
1\/2\u2033<\/th>\n14<\/td>\n8.16<\/td>\n4.50<\/td>\n13.16<\/td>\n12.70<\/td>\n15.00<\/td>\n9.10<\/td>\n5.02<\/td>\n<\/tr>\n
3\/4\u2033<\/th>\n14<\/td>\n9.53<\/td>\n5.25<\/td>\n14.53<\/td>\n14.10<\/td>\n16.30<\/td>\n10.20<\/td>\n5.62<\/td>\n<\/tr>\n
1\u2033<\/th>\n11<\/td>\n10.39<\/td>\n4.50<\/td>\n16.79<\/td>\n16.20<\/td>\n19.10<\/td>\n11.60<\/td>\n5.02<\/td>\n<\/tr>\n
1-1\/4\u2033<\/th>\n11<\/td>\n12.70<\/td>\n5.50<\/td>\n19.10<\/td>\n18.50<\/td>\n21.40<\/td>\n13.40<\/td>\n5.80<\/td>\n<\/tr>\n
1-1\/2\u2033<\/th>\n11<\/td>\n12.70<\/td>\n5.50<\/td>\n19.10<\/td>\n18.50<\/td>\n21.40<\/td>\n13.40<\/td>\n5.80<\/td>\n<\/tr>\n
2\u2033<\/th>\n11<\/td>\n15.88<\/td>\n6.88<\/td>\n23.38<\/td>\n22.80<\/td>\n25.70<\/td>\n16.90<\/td>\n7.32<\/td>\n<\/tr>\n
2-1\/2\u2033<\/th>\n11<\/td>\n17.46<\/td>\n7.56<\/td>\n26.66<\/td>\n26.70<\/td>\n30.10<\/td>\n18.60<\/td>\n8.06<\/td>\n<\/tr>\n
3\u2033<\/th>\n11<\/td>\n20.64<\/td>\n8.94<\/td>\n29.84<\/td>\n29.80<\/td>\n33.30<\/td>\n21.10<\/td>\n9.14<\/td>\n<\/tr>\n
4\u2033<\/th>\n11<\/td>\n25.40<\/td>\n11.00<\/td>\n35.80<\/td>\n35.80<\/td>\n39.30<\/td>\n25.90<\/td>\n11.22<\/td>\n<\/tr>\n
5\u2033<\/th>\n11<\/td>\n28.58<\/td>\n12.38<\/td>\n40.08<\/td>\n40.10<\/td>\n43.50<\/td>\n29.30<\/td>\n12.69<\/td>\n<\/tr>\n
6\u2033<\/th>\n11<\/td>\n28.58<\/td>\n12.38<\/td>\n40.08<\/td>\n40.10<\/td>\n43.50<\/td>\n29.30<\/td>\n12.69<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n\n\n

Table 6. BSPT thread diameters (mm)<\/h3>\n\n\n\n
\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Taille<\/th>\nPipe OD<\/th>\n\u00d8D0 (pipe end)<\/th>\n\u00d8D2 (end of a + f)<\/th>\n\u00d8D1 (gauge plane)<\/th>\n\u00d8D3 (at t)<\/th>\n\u00d8D4 (at \u2113)<\/th>\n<\/tr>\n<\/thead>\n
1\/8\u2033<\/th>\n10.5<\/td>\n9.48<\/td>\n9.88<\/td>\n8.57<\/td>\n8.29<\/td>\n8.18<\/td>\n<\/tr>\n
1\/4\u2033<\/th>\n13.8<\/td>\n12.78<\/td>\n13.39<\/td>\n11.45<\/td>\n11.03<\/td>\n10.86<\/td>\n<\/tr>\n
3\/8\u2033<\/th>\n17.3<\/td>\n16.27<\/td>\n16.89<\/td>\n14.95<\/td>\n14.51<\/td>\n14.34<\/td>\n<\/tr>\n
1\/2\u2033<\/th>\n21.7<\/td>\n20.45<\/td>\n21.27<\/td>\n18.63<\/td>\n18.06<\/td>\n17.84<\/td>\n<\/tr>\n
3\/4\u2033<\/th>\n27.2<\/td>\n25.85<\/td>\n26.75<\/td>\n24.12<\/td>\n23.48<\/td>\n23.24<\/td>\n<\/tr>\n
1\u2033<\/th>\n34.0<\/td>\n32.60<\/td>\n33.65<\/td>\n30.29<\/td>\n29.57<\/td>\n29.28<\/td>\n<\/tr>\n
1-1\/4\u2033<\/th>\n42.7<\/td>\n41.12<\/td>\n42.31<\/td>\n38.95<\/td>\n38.11<\/td>\n37.80<\/td>\n<\/tr>\n
1-1\/2\u2033<\/th>\n48.6<\/td>\n47.01<\/td>\n48.20<\/td>\n44.85<\/td>\n44.01<\/td>\n43.69<\/td>\n<\/tr>\n
2\u2033<\/th>\n60.5<\/td>\n58.62<\/td>\n60.08<\/td>\n56.66<\/td>\n55.60<\/td>\n55.23<\/td>\n<\/tr>\n
2-1\/2\u2033<\/th>\n76.3<\/td>\n74.09<\/td>\n75.76<\/td>\n72.23<\/td>\n71.06<\/td>\n70.56<\/td>\n<\/tr>\n
3\u2033<\/th>\n89.1<\/td>\n86.59<\/td>\n88.46<\/td>\n84.93<\/td>\n83.61<\/td>\n83.06<\/td>\n<\/tr>\n
4\u2033<\/th>\n114.3<\/td>\n111.44<\/td>\n113.68<\/td>\n110.07<\/td>\n108.45<\/td>\n107.83<\/td>\n<\/tr>\n
5\u2033<\/th>\n139.8<\/td>\n136.64<\/td>\n139.15<\/td>\n135.47<\/td>\n133.64<\/td>\n132.97<\/td>\n<\/tr>\n
6\u2033<\/th>\n165.2<\/td>\n162.04<\/td>\n164.55<\/td>\n160.87<\/td>\n159.04<\/td>\n158.37<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n\n\n

Table 7. BSPP (G, PF) basic diameters, JIS B 0202 and ISO 228-1 (mm)<\/h3>\n\n\n\n

BSPP shares n, p and h with BSPT at every size, and the same major, pitch and minor diameters as BSPT at its gauge plane. Because the thread is parallel there is no gauge length and no taper diameter: the basic diameters apply along the whole thread.<\/p>\n\n\n\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Taille<\/th>\nn<\/th>\np<\/th>\nh<\/th>\nMajor diameter d<\/th>\nPitch diameter d2<\/th>\nMinor diameter d1<\/th>\n<\/tr>\n<\/thead>\n
1\/8\u2033<\/th>\n28<\/td>\n0.907<\/td>\n0.581<\/td>\n9.728<\/td>\n9.147<\/td>\n8.566<\/td>\n<\/tr>\n
1\/4\u2033<\/th>\n19<\/td>\n1.337<\/td>\n0.856<\/td>\n13.157<\/td>\n12.301<\/td>\n11.445<\/td>\n<\/tr>\n
3\/8\u2033<\/th>\n19<\/td>\n1.337<\/td>\n0.856<\/td>\n16.662<\/td>\n15.806<\/td>\n14.950<\/td>\n<\/tr>\n
1\/2\u2033<\/th>\n14<\/td>\n1.814<\/td>\n1.162<\/td>\n20.955<\/td>\n19.793<\/td>\n18.631<\/td>\n<\/tr>\n
3\/4\u2033<\/th>\n14<\/td>\n1.814<\/td>\n1.162<\/td>\n26.441<\/td>\n25.279<\/td>\n24.117<\/td>\n<\/tr>\n
1\u2033<\/th>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\n33.249<\/td>\n31.770<\/td>\n30.291<\/td>\n<\/tr>\n
1-1\/4\u2033<\/th>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\n41.910<\/td>\n40.431<\/td>\n38.952<\/td>\n<\/tr>\n
1-1\/2\u2033<\/th>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\n47.803<\/td>\n46.324<\/td>\n44.845<\/td>\n<\/tr>\n
2\u2033<\/th>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\n59.614<\/td>\n58.135<\/td>\n56.656<\/td>\n<\/tr>\n
2-1\/2\u2033<\/th>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\n75.184<\/td>\n73.705<\/td>\n72.226<\/td>\n<\/tr>\n
3\u2033<\/th>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\n87.884<\/td>\n86.405<\/td>\n84.926<\/td>\n<\/tr>\n
4\u2033<\/th>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\n113.030<\/td>\n111.551<\/td>\n110.072<\/td>\n<\/tr>\n
5\u2033<\/th>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\n138.430<\/td>\n136.951<\/td>\n135.472<\/td>\n<\/tr>\n
6\u2033<\/th>\n11<\/td>\n2.309<\/td>\n1.479<\/td>\n163.830<\/td>\n162.351<\/td>\n160.872<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n\n\n

NPT vs BSPT vs BSPP: which threads fit together<\/h2>\n\n\n\n

NPT and BSPT do not seal against each other at any size, even at 1\/2\u2033 and 3\/4\u2033 where they screw together. BSPP does not seal against either taper thread, because it does not seal on the thread at all. The one parallel female thread meant to seal with a BSPT male is Rp, which belongs to ISO 7-1 and JIS B 0203, not to the G thread of BSPP.<\/p>\n\n\n\n

Two things keep NPT and BSPT apart. The first is the pitch pattern in Table 1: at most sizes the threads per inch differ, so the parts bind within a few turns. The second is the thread angle, 60\u00b0 against 55\u00b0, and it is the one that causes trouble, because at 1\/2\u2033 and 3\/4\u2033 the pitches match and the parts run together by hand. With a 5\u00b0 difference in thread angle (2.5\u00b0 on each flank), the flanks do not lie on each other, so a helical gap runs the length of the engagement. Sealant may hide the gap at first; it does not remove it.<\/p>\n\n\n\n

Parallel against taper fails for a different reason. A G or PF external thread in an Rc female contacts only over the last turn at the leading end of the male, where the diameters meet, with clearance along the rest of the engagement. An R or PT external thread in a G female is closer to workable, since the pitch and angle match, but the G thread of ISO 228-1 has its own tolerances and, by that standard’s own scope, is not meant to make a pressure-tight joint on the thread. If a parallel female thread has to seal with a taper male, specify Rp, not G.<\/p>\n\n\n\n

How to identify a pipe thread on a valve or fitting<\/h2>\n\n\n\n

Three measurements settle it. The outside diameter of the male thread gives the nominal size; the number of threads per inch separates NPT from BSP at every size except 1\/2\u2033 and 3\/4\u2033; and the thread angle, or the presence of a taper, separates the rest. Compare each reading with the chart.<\/p>\n\n\n\n

Start with the outside diameter, measured with calipers at the first full thread near the pipe end (the \u00d8D0 column), or on the pipe itself (the OD column). The nominal size is not the diameter: a 1\/2\u2033 pipe thread measures about 21 mm, a 1\u2033 thread about 33 mm. From 1\/8\u2033 to 2\u2033, and at 3\u2033, the NPT and BSPT \u00d8D0 values at the same nominal size are within a millimeter of each other, so this step identifies the size, not the standard. At 2-1\/2\u2033, 4\u2033, 5\u2033 and 6\u2033 the \u00d8D0 values differ by 1.2 to 4.2 mm, so compare the reading with both columns.<\/p>\n\n\n\n

Next, count the threads per inch with a pitch gauge, or count the thread crests over 25.4 mm. Read the result against Table 1. A count of 27, 18, 11.5 or 8 is NPT; 28, 19 or 11 is BSP. A count of 14 is either, at 1\/2\u2033 or 3\/4\u2033, and needs the third check.<\/p>\n\n\n\n

For the third check, a 55\u00b0 and 60\u00b0 thread angle gauge is the direct way; held against the thread in good light, the wrong angle shows a gap at the flank. If no gauge is at hand, the taper gives a second clue, though it does not separate NPT from BSPT: a taper thread changes about 1 mm in diameter for every 16 mm of length, so calipers at the first and last full thread read differently, while a parallel thread reads the same. A taper male thread also stops after a few turns when run by hand into its matching female, four to seven turns on sizes up to 2\u2033 (the basic values in the a column, in threads), while a parallel thread runs in to the end. Then check the marking: R, Rc, PT or BSPT on a drawing means the 55\u00b0 taper thread; G, PF or BSPP means the 55\u00b0 parallel thread; NPT means NPT.<\/p>\n\n\n\n

For tube fittings, port threads and the less common straight threads, the Swagelok thread and end connection identification guide<\/a> (PDF) goes through the same procedure step by step, with reference tables for each type.<\/p>\n\n\n\n

Which pipe thread to specify on a stainless steel valve or fitting<\/h2>\n\n\n\n

Specify the thread by its standard and designation on the RFQ: 1\/2 NPT, Rc 1\/2 (PT 1\/2) or G 1\/2 (PF 1\/2), and say which end of a valve is male and which is female. We are Yzng Trong, a stainless steel ball valve manufacturer in Taichung, Taiwan, making valves since 1999. Our threaded ball valves are made in PT (the JIS name for BSPT), NPT or PF (the JIS name for BSPP), to the thread stated on the order; the threaded pipe fittings on this site are PT. The thread is cut when the valve is made and cannot be changed afterwards, so the RFQ is the moment to settle it.<\/p>\n\n\n\n

Four situations cover most orders. A plant in the United States or Canada runs on NPT, so ask for NPT and write it on the order; the valve will then mate with any NPT fitting in the plant. A plant in Taiwan or Japan runs on PT, and much of Asia on the same thread under its ISO names R and Rc; a PT valve mates with the Rc and Rp fittings already installed, and it is the thread to ask for when replacing a valve that came from Taiwan or Japan. A plant that seals on a face with bonded washers or O-rings uses PF, and the mating part must be the parallel thread too.<\/p>\n\n\n\n

The fourth situation is the one the identification section above exists for: a female fitting is already installed and nobody is sure what it is. Measure it before ordering. A valve in the wrong thread cannot be reworked into the right one, and an adapter adds a joint, which is one more place for a leak. Our guide to raccords d'extr\u00e9mit\u00e9 de vanne<\/a> covers when a threaded end is the right choice at all, against socket weld and butt weld ends; threaded ends are the usual choice on small-bore lines. The threaded ball valves listed below are rated 1000 WOG, a cold working pressure that our WOG rating guide<\/a> explains.<\/p>\n\n\n\n

The threaded models on this site are the seal-welded two-piece ball valve (V-2B)<\/a> in 1\/4\u2033 to 3\u2033, with a 4\u2033 version that uses a bolted end cap, the one-piece ball valve (R-1B)<\/a> in 1\/4\u2033 to 3\u2033, the three-piece ball valve with threaded or socket weld ends<\/a> in 1\/4\u2033 to 4\u2033, and a male-by-female ball valve<\/a> for the cases where the valve itself replaces a nipple. Threaded raccords pour tuyaux en acier inoxydable<\/a>, such as the PT pipe coupling<\/a>, are listed in their own category. The valve RFQ guide<\/a> lists the other items an inquiry should carry, from quantity to delivery date and destination.<\/p>\n\n\n\n

Common pipe thread mistakes<\/h2>\n\n\n\n

The mistakes below are the ones that produce leaking joints or valves that cannot be installed. Most of them come from treating NPT and BSP as one family, or a nominal size as a measurement.<\/p>\n\n\n\n