API 5B — Thread Dimensions
Thread dimensions for API round thread casing (STC and LTC), buttress casing (BTC), line pipe thread, and tubing thread (non-upset, external-upset and integral-joint) per API Specification 5B, 16th Edition. 102 rows across 7 tables — L1, L2, L4, pitch diameter, makeup and minimum full-crest thread.
Two things most sources get wrong
There is no single API thread taper. Buttress casing thread is tapered 3/4 in per foot up to 13⅜ in, and 1 in per foot at 16 in and larger (API 5B Table 5). Round thread casing, line pipe thread and tubing thread are 3/4 in per foot. Quoting one taper for every API thread gets 16 in, 18⅝ in and 20 in buttress connections wrong.
0.017 in and 0.020 in are truncations, not radii. For the 8 TPI casing round thread form, 0.017 in is the root truncation (Srs, Srn) and 0.020 in is the crest truncation (Scs, Scn) — API 5B Table 11. Truncation is material removed from a theoretically sharp profile; a radius is a different quantity, and gauges set up on that reading will not conform.
API Specification 5B covers the threading, gauging and thread inspection of casing, tubing and line pipe. It is the companion to API 5CT, which specifies the pipe body: 5CT tells you what a 9⅝ in 47 lb/ft P110 joint is made of, 5B tells you what the thread cut on its ends must measure.
L4 — total thread length from pipe end to vanish point — is the dimension the API 5C3 joint-strength formula consumes, which is why these tables sit underneath the joint strength calculator.
Source: API Specification 5B, 16th Edition — December 2017 (Errata 1 2018, Errata 2 2018, Addendum 1 2018). All dimensions in inches. Verified 2026-10-07.
Thread Forms and Taper
| Form | TPI | Pitch (in) | Taper | Source |
|---|---|---|---|---|
| casing round 8tpi | 8 | 0.125 | 3/4 (0.0625 in/in); 1 in/ft option on larger casing | Table 11 |
| line pipe thread | 27 → 8 by size | — | 0.75 in/ft | Table 13 |
| tubing round 10tpi | 10 | 0.1 | 0.75 in/ft | Table 15 |
| buttress | 5 | — | 3/4 for <=13 3/8 in; 1 in/ft for 16 in and larger | Table 5 / Section 5 |
Casing round thread form also defines thread height H = 0.10825 in, sharp height hs/hn = 0.07125 in, root truncation 0.017 in and crest truncation 0.02 in. Tubing thread is 10 TPI — 8 TPI on 4 1/2 in tubing.
Casing — Short Round Thread (STC)
API round thread, 8 TPI. Dimensions vary by weight on the lighter casing sizes.
API 5B Table 1 — 8 TPI. Lc = L4 - 1.125 in (except size 20, footnote exception). Dimensions vary by weight for some light casing.
| Size | OD (in) | Weight (lb/ft) | TPI | L1 (in) | L2 (in) | L4 (in) | E1 (in) | M (in) | Lc min (in) |
|---|---|---|---|---|---|---|---|---|---|
| 4 1/2 | 4.500 | 9.50 | 8 | 0.921 | 1.715 | 2.000 | 4.40337 | 1.125 | 0.875 |
| 4 1/2 | 4.500 | other weights | 8 | 1.546 | 2.340 | 2.625 | 4.40337 | 0.500 | 1.500 |
| 5 | 5.000 | 11.50 | 8 | 1.421 | 2.215 | 2.500 | 4.90337 | 0.750 | 1.375 |
| 5 | 5.000 | other weights | 8 | 1.671 | 2.465 | 2.750 | 4.90337 | 0.500 | 1.625 |
| 5 1/2 | 5.500 | all weights | 8 | 1.796 | 2.590 | 2.875 | 5.40337 | 0.500 | 1.750 |
| 6 5/8 | 6.625 | all weights | 8 | 2.046 | 2.840 | 3.125 | 6.52837 | 0.500 | 2.000 |
| 7 | 7.000 | 17.00 | 8 | 1.296 | 2.090 | 2.375 | 6.90337 | 1.250 | 1.250 |
| 7 | 7.000 | other weights | 8 | 2.046 | 2.840 | 3.125 | 6.90337 | 0.500 | 2.000 |
| 7 5/8 | 7.625 | all weights | 8 | 2.104 | 2.965 | 3.250 | 7.52418 | 0.500 | 2.125 |
| 8 5/8 | 8.625 | 24.00 | 8 | 1.854 | 2.715 | 3.000 | 8.52418 | 0.875 | 1.875 |
| 8 5/8 | 8.625 | other weights | 8 | 2.229 | 3.090 | 3.375 | 8.52418 | 0.500 | 2.250 |
| 9 5/8 | 9.625 | all weights | 8 | 2.229 | 3.090 | 3.375 | 9.52418 | 0.500 | 2.250 |
| 9 5/8 | 9.625 | all weights | 8 | 2.162 | 3.090 | 3.375 | 9.51999 | 0.500 | 2.250 |
| 10 3/4 | 10.750 | 32.75 | 8 | 1.604 | 2.465 | 2.750 | 10.64918 | 1.250 | 1.625 |
| 10 3/4 | 10.750 | other weights | 8 | 2.354 | 3.215 | 3.500 | 10.64918 | 0.500 | 2.375 |
| 10 3/4 | 10.750 | other weights | 8 | 2.287 | 3.215 | 3.500 | 10.64499 | 0.500 | 2.375 |
| 11 3/4 | 11.750 | all weights | 8 | 2.354 | 3.215 | 3.500 | 11.64918 | 0.500 | 2.375 |
| 11 3/4 | 11.750 | all weights | 8 | 2.287 | 3.215 | 3.500 | 11.64499 | 0.500 | 2.375 |
| 13 3/8 | 13.375 | all weights | 8 | 2.354 | 3.215 | 3.500 | 13.27418 | 0.500 | 2.375 |
| 13 3/8 | 13.375 | all weights | 8 | 2.287 | 3.215 | 3.500 | 13.26999 | 0.500 | 2.375 |
| 16 | 16.000 | all weights | 8 | 2.854 | 3.715 | 4.000 | 15.89918 | 0.500 | 2.875 |
| 18 5/8 | 18.625 | 87.50 | 8 | 2.854 | 3.715 | 4.000 | 18.52418 | 0.500 | 2.875 |
| 20 | 20.000 | all weights | 8 | 2.854 | 3.715 | 4.000 | 19.89918 | 0.500 | 2.785 |
| 20 | 20.000 | all weights | 8 | 2.787 | 3.715 | 4.000 | 19.89499 | 0.500 | 2.875 |
Casing — Long Round Thread (LTC)
Same thread form as STC with a longer engagement — L4 is one inch greater at 4½ in.
API 5B Table 4 — 8 TPI. Lc = L4 - 1.125 in.
| Size | OD (in) | Weight (lb/ft) | TPI | L1 (in) | L2 (in) | L4 (in) | E1 (in) | M (in) | Lc min (in) |
|---|---|---|---|---|---|---|---|---|---|
| 4 1/2 | 4.500 | all weights | 8 | 1.921 | 2.715 | 3.000 | 4.40337 | 0.500 | 1.875 |
| 5 | 5.000 | all weights | 8 | 2.296 | 3.090 | 3.375 | 4.90337 | 0.500 | 2.250 |
| 5 1/2 | 5.500 | all weights | 8 | 2.421 | 3.215 | 3.500 | 5.40337 | 0.500 | 2.375 |
| 6 5/8 | 6.625 | all weights | 8 | 2.796 | 3.590 | 3.875 | 6.52837 | 0.500 | 2.750 |
| 7 | 7.000 | all weights | 8 | 2.921 | 3.715 | 4.000 | 6.90337 | 0.500 | 2.875 |
| 7 5/8 | 7.625 | all weights | 8 | 2.979 | 3.840 | 4.125 | 7.52418 | 0.500 | 3.000 |
| 8 5/8 | 8.625 | all weights | 8 | 3.354 | 4.215 | 4.500 | 8.52418 | 0.500 | 3.375 |
| 9 5/8 | 9.625 | all weights | 8 | 3.604 | 4.465 | 4.750 | 9.52418 | 0.500 | 3.625 |
| 9 5/8 | 9.625 | all weights | 8 | 3.537 | 4.465 | 4.750 | 9.51999 | 0.500 | 3.625 |
| 20 | 20.000 | all weights | 8 | 4.104 | 4.965 | 5.250 | 19.89918 | 0.500 | 4.125 |
| 20 | 20.000 | all weights | 8 | 4.037 | 4.965 | 5.250 | 19.89499 | 0.500 | 4.125 |
Casing — Buttress Thread (BTC)
Five TPI. The major diameter D4 exceeds pipe OD on every size up to 13⅜ in, and equals it at 16 in and above.
API 5B Table 5 — 5 TPI. Buttress thread; major diameter D4 exceeds pipe OD. L7 = complete-thread length.
| Size | D4 major (in) | TPI | g (in) | L7 (in) | L4 (in) | E7 (in) | M (in) | Lc min (in) |
|---|---|---|---|---|---|---|---|---|
| 4 1/2 | 4.516 | 5 | 1.984 | 1.6535 | 3.6375 | 4.454 | 1.884 | 1.2535 |
| 5 | 5.016 | 5 | 1.984 | 1.7785 | 3.7625 | 4.954 | 1.784 | 1.3785 |
| 5 1/2 | 5.516 | 5 | 1.984 | 1.8410 | 3.8250 | 5.454 | 1.784 | 1.4410 |
| 6 5/8 | 6.641 | 5 | 1.984 | 2.0285 | 4.0125 | 6.579 | 1.784 | 1.6285 |
| 7 | 7.016 | 5 | 1.984 | 2.2160 | 4.2000 | 6.954 | 1.784 | 1.8160 |
| 7 5/8 | 7.641 | 5 | 1.984 | 2.4035 | 4.3875 | 7.579 | 1.784 | 2.0035 |
| 8 5/8 | 8.641 | 5 | 1.984 | 2.5285 | 4.5125 | 8.579 | 1.784 | 2.1285 |
| 9 5/8 | 9.641 | 5 | 1.984 | 2.5285 | 4.5125 | 9.579 | 1.784 | 2.1285 |
| 10 3/4 | 10.766 | 5 | 1.984 | 2.5285 | 4.5125 | 10.704 | 1.784 | 2.1285 |
| 11 3/4 | 11.766 | 5 | 1.984 | 2.5285 | 4.5125 | 11.704 | 1.784 | 2.1285 |
| 13 3/8 | 13.391 | 5 | 1.984 | 2.5285 | 4.5125 | 13.329 | 1.784 | 2.1285 |
| 16 | 16.000 | 5 | 1.488 | 3.1245 | 4.6125 | 15.938 | 1.313 | 2.7245 |
| 18 5/8 | 18.625 | 5 | 1.488 | 3.1245 | 4.6125 | 18.563 | 1.313 | 2.7245 |
| 20 | 20.000 | 5 | 1.488 | 3.1245 | 4.6125 | 19.938 | 1.313 | 2.7245 |
Line Pipe Thread
Tapered NPT-form thread. TPI falls from 27 at NPS ⅛ to 8 at the large sizes.
API 5B Table 3 — TPI varies 27->8 by size. Lc = L4 - 0.652 in (11 1/2 TPI) or L4 - 0.937 in (8 TPI); small sizes have no Lc.
| NPS | OD (in) | TPI | L1 (in) | L2 (in) | L4 (in) | E1 (in) | J (in) | M (in) | Lc min (in) |
|---|---|---|---|---|---|---|---|---|---|
| 1/8 | 0.405 | 27 | 0.1615 | 0.2639 | 0.3924 | 0.37360 | 0.1389 | 0.1198 | — |
| 1/4 | 0.540 | 18 | 0.2278 | 0.4018 | 0.5946 | 0.49163 | 0.2179 | 0.2001 | — |
| 3/8 | 0.675 | 18 | 0.2400 | 0.4078 | 0.6006 | 0.62701 | 0.2110 | 0.1938 | — |
| 1/2 | 0.840 | 14 | 0.3200 | 0.5337 | 0.7815 | 0.77843 | 0.2690 | 0.2473 | — |
| 3/4 | 1.050 | 14 | 0.3390 | 0.5457 | 0.7935 | 0.98887 | 0.2803 | 0.2403 | — |
| 1 | 1.315 | 11.5 | 0.4000 | 0.6828 | 0.9845 | 1.25863 | 0.3285 | 0.3235 | 0.3325 |
| 1 1/4 | 1.660 | 11.5 | 0.4200 | 0.7065 | 1.0085 | 1.58338 | 0.3665 | 0.3275 | 0.3565 |
| 1 1/2 | 1.900 | 11.5 | 0.4200 | 0.7235 | 1.0255 | 1.82234 | 0.3498 | 0.3442 | 0.3735 |
| 2 | 2.375 | 11.5 | 0.4360 | 0.7565 | 1.0582 | 2.29627 | 0.3793 | 0.3611 | 0.4062 |
| 2 1/2 | 2.875 | 8 | 0.6820 | 1.1375 | 1.5712 | 2.76216 | 0.4913 | 0.6397 | 0.6342 |
| 3 | 3.500 | 8 | 0.7660 | 1.2000 | 1.6337 | 3.38850 | 0.5038 | 0.6127 | 0.6967 |
| 3 1/2 | 4.000 | 8 | 0.8210 | 1.2500 | 1.6837 | 3.88881 | 0.5163 | 0.6537 | 0.7467 |
| 4 | 4.500 | 8 | 0.8440 | 1.3000 | 1.7337 | 4.38712 | 0.4725 | 0.7382 | 0.7967 |
| 5 | 5.563 | 8 | 0.9370 | 1.4063 | 1.8400 | 5.44929 | 0.4913 | 0.8332 | 0.9030 |
| 6 | 6.625 | 8 | 0.9580 | 1.5125 | 1.9462 | 6.50597 | 0.4788 | 0.8987 | 1.0092 |
| 8 | 8.625 | 8 | 1.0630 | 1.7125 | 2.1462 | 8.50003 | 0.5163 | 0.8717 | 1.2092 |
| 10 | 10.750 | 8 | 1.2100 | 1.9250 | 2.3587 | 10.62003 | 0.5038 | 0.8217 | 1.4217 |
| 12 | 12.750 | 8 | 1.3600 | 2.1250 | 2.5587 | 12.61781 | 0.5038 | 0.8337 | 1.6217 |
| 14D | 14.000 | 8 | 1.5620 | 2.2500 | 2.6837 | 13.87263 | 0.4913 | 0.8717 | 1.7467 |
| 16D | 16.000 | 8 | 1.8120 | 2.4500 | 2.8837 | 15.87575 | 0.4788 | 0.8217 | 1.9467 |
| 18D | 18.000 | 8 | 2.0000 | 2.6500 | 3.0837 | 17.87500 | 0.4788 | 0.8337 | 2.1467 |
| 20D | 20.000 | 8 | 2.1250 | 2.8500 | 3.2837 | 19.87031 | 0.5288 | 0.9087 | 2.3467 |
Tubing — Non-Upset (NU)
Box OD equals pipe OD — the coupling is cut on unupset pipe body.
API 5B Table 6 — 10 TPI (8 TPI on 4 1/2 in). Lc = L4 - 0.900 in (>=0.300) for 10 TPI; L4 - 1.000 in for 8 TPI.
| Pipe OD (in) | Box OD D4 (in) | TPI | L1 (in) | L2 (in) | L4 (in) | E1 (in) | M (in) | Lc min (in) |
|---|---|---|---|---|---|---|---|---|
| 1.050 | 1.050 | 10 | 0.448 | 0.925 | 1.094 | 0.98826 | 0.446 | 0.300 |
| 1.315 | 1.315 | 10 | 0.479 | 0.956 | 1.125 | 1.25328 | 0.446 | 0.300 |
| 1.660 | 1.660 | 10 | 0.604 | 1.081 | 1.250 | 1.59826 | 0.446 | 0.350 |
| 1.900 | 1.900 | 10 | 0.729 | 1.206 | 1.375 | 1.83826 | 0.446 | 0.475 |
| 2.375 | 2.375 | 10 | 0.979 | 1.456 | 1.625 | 2.31326 | 0.446 | 0.725 |
| 2.875 | 2.875 | 10 | 1.417 | 1.894 | 2.063 | 2.81326 | 0.446 | 1.163 |
| 3.500 | 3.500 | 10 | 1.667 | 2.144 | 2.313 | 3.43826 | 0.446 | 1.413 |
| 4.000 | 4.000 | 8 | 1.591 | 2.140 | 2.375 | 3.91395 | 0.534 | 1.375 |
| 4.500 | 4.500 | 8 | 1.779 | 2.328 | 2.563 | 4.41395 | 0.534 | 1.563 |
Tubing — External Upset (EU)
The pipe end is upset before threading, so box OD is larger than pipe OD at every size.
API 5B Table 7 — External-upset; box_od_D4 is the upset OD. Same Lc rule as NU.
| Pipe OD (in) | Box OD D4 (in) | TPI | L1 (in) | L2 (in) | L4 (in) | E1 (in) | M (in) | Lc min (in) |
|---|---|---|---|---|---|---|---|---|
| 1.050 | 1.315 | 10 | 0.479 | 0.956 | 1.125 | 1.25328 | 0.446 | 0.300 |
| 1.315 | 1.469 | 10 | 0.604 | 1.081 | 1.250 | 1.40706 | 0.446 | 0.350 |
| 1.660 | 1.812 | 10 | 0.729 | 1.206 | 1.375 | 1.75079 | 0.446 | 0.475 |
| 1.900 | 2.094 | 10 | 0.792 | 1.269 | 1.438 | 2.03206 | 0.446 | 0.538 |
| 2.375 | 2.594 | 8 | 1.154 | 1.703 | 1.938 | 2.50775 | 0.534 | 0.938 |
| 2.875 | 3.094 | 8 | 1.341 | 1.890 | 2.125 | 3.00775 | 0.534 | 1.125 |
| 3.500 | 3.750 | 8 | 1.591 | 2.140 | 2.375 | 3.66395 | 0.534 | 1.375 |
| 4.000 | 4.250 | 8 | 1.716 | 2.265 | 2.500 | 4.16395 | 0.534 | 1.500 |
| 4.500 | 4.750 | 8 | 1.841 | 2.390 | 2.625 | 4.66395 | 0.534 | 1.625 |
Tubing — Integral Joint (IJ)
No separate coupling — the box is formed in the pipe end itself.
API 5B Table 9 — Integral joint; box_od_D4 is the upset box OD.
| Pipe OD (in) | Box OD D4 (in) | TPI | L1 (in) | L2 (in) | L4 (in) | E1 (in) | M (in) | Lc min (in) |
|---|---|---|---|---|---|---|---|---|
| 1.050 | 1.315 | 10 | 0.979 | 1.456 | 1.625 | 1.25328 | 0.446 | 0.725 |
| 1.315 | 1.469 | 10 | 1.104 | 1.581 | 1.750 | 1.40706 | 0.446 | 0.850 |
| 1.660 | 1.812 | 10 | 1.229 | 1.706 | 1.875 | 1.75079 | 0.446 | 0.975 |
| 1.900 | 2.094 | 10 | 1.417 | 1.894 | 2.063 | 2.03206 | 0.446 | 1.163 |
| 2.375 | 2.594 | 8 | 1.779 | 2.328 | 2.563 | 2.50775 | 0.534 | 1.563 |
| 2.875 | 3.094 | 8 | 2.091 | 2.640 | 2.875 | 3.00775 | 0.534 | 1.875 |
| 3.500 | 3.750 | 8 | 2.341 | 2.890 | 3.125 | 3.66395 | 0.534 | 2.125 |
| 4.000 | 4.250 | 8 | 2.591 | 3.140 | 3.375 | 4.16395 | 0.534 | 2.375 |
| 4.500 | 4.750 | 8 | 2.716 | 3.265 | 3.500 | 4.66395 | 0.534 | 2.500 |
| 1.315 | 1.315 | 10 | 0.479 | 0.956 | 1.125 | 1.25328 | 0.446 | 0.225 |
| 1.660 | 1.660 | 10 | 0.604 | 1.081 | 1.250 | 1.59826 | 0.446 | 0.350 |
| 1.900 | 1.900 | 10 | 0.729 | 1.206 | 1.375 | 1.83826 | 0.446 | 0.475 |
| 2.063 | 2.094 | 10 | 0.792 | 1.269 | 1.438 | 2.03206 | 0.446 | 0.538 |
Column Key
| Symbol | Definition |
|---|---|
| L1 | Length, pipe end to hand-tight plane |
| L2 | Length of effective (full-form) thread |
| L4 | Total length, pipe end to vanish point (total thread length) |
| L7 | Length of complete (perfect) thread — buttress |
| pitch dia E1 | Pitch diameter at the hand-tight plane (round/line pipe) |
| pitch dia E7 | Pitch diameter at plane E7 — buttress |
| M | Length, coupling face relationship at makeup (see API 5B figures) |
| Lc min full thread | Minimum length of full-crest thread from pipe end (relates to L4 by grade footnote) |
| g imperfect threads | Length allowance for imperfect threads at the vanish point — buttress |
| major dia D4 in | Major (large-end) thread diameter |
| box od D4 in | Coupling/box outside diameter (tubing) or major diameter |
Notes
- Units are inches. API 5B tabulates in inches only — there is no SI annex as there is in API 5CT. Convert from these values directly rather than from a secondary metric table.
- Buttress taper changes with size: 3/4 in/ft to 13⅜ in, 1 in/ft at 16 in and above. The major diameter D4 reflects this — it exceeds pipe OD below 16 in and equals it at and above.
- Tubing pitch is not uniform. Non-upset runs 10 TPI through 3½ in and 8 TPI at 4 in and 4½ in; external-upset switches to 8 TPI from 2⅜ in upward. The two differ at 2⅜ in, 2⅞ in, 3½ in.
- L4 feeds joint strength. API 5C3 consumes total thread length; the joint strength calculator reads these same values.
- For pipe body dimensions, grades and which connections exist in which size, see API 5CT. For line pipe, see API 5L.
- ZC Steel Pipe supplies threaded product to these dimensions. This page is an engineering reference compiled from the published standard; it is not a substitute for the standard itself, which should be purchased from API.
Frequently Asked Questions
Do all API 5B threads use a 3/4 inch per foot taper?
No, and this is the most commonly repeated error about API threads. Buttress casing thread is tapered 3/4 in/ft for sizes up to and including 13 3/8 in, but 1 in/ft for 16 in and larger — API 5B Table 5. API round thread casing (STC and LTC) is 3/4 in/ft, which is 0.0625 in/in, with a 1 in/ft option on larger casing. Line pipe thread and tubing thread are both 3/4 in/ft. Applying a single taper across all sizes gives the wrong geometry for 16 in, 18 5/8 in and 20 in buttress connections. The dimensional consequence is visible in the tables above: the buttress major diameter D4 exceeds pipe OD at every size up to 13 3/8 in (9 5/8 in casing has D4 = 9.641 in) but equals nominal OD at 16, 18 5/8 and 20 in.
What do L1, L2, L4 and Lc mean on an API thread drawing?
L1 is the length from the pipe end to the hand-tight plane. L2 is the length of effective, full-form thread. L4 is the total thread length, measured from the pipe end to the vanish point, and it is the value the API 5C3 joint-strength formula consumes. Lc is the minimum length of full-crest thread measured from the pipe end. For API round thread casing, Lc = L4 − 1.125 in. For line pipe the relationship depends on pitch: L4 − 0.652 in at 11 1/2 TPI and L4 − 0.937 in at 8 TPI, and the smallest sizes have no Lc value at all. On buttress connections L7 replaces L2 as the length of complete thread, and g is the allowance for imperfect threads at the vanish point.
Are the API 5B values 0.017 and 0.020 thread root and crest radii?
No. For the 8 TPI casing round thread form, 0.017 in is the root truncation (Srs and Srn) and 0.020 in is the crest truncation (Scs and Scn) — API 5B Table 11. Truncation is the amount removed from a theoretically sharp thread profile, not a radius. The same table gives thread height H = 0.10825 in and sharp height hs/hn = 0.07125 in at a pitch of 0.125 in. Sources that present these two figures as radii are describing a different geometric quantity, and gauge or machining work set up on that basis will not produce a conforming thread.
Why will a 2 7/8 inch non-upset tubing pin not enter an external-upset coupling?
Because they are cut at different pitches at that size. API 5B tubing thread is nominally 10 TPI, but the two forms change to 8 TPI at different diameters: non-upset tubing runs 10 TPI up to and including 3 1/2 in and switches to 8 TPI at 4 in, while external-upset tubing switches to 8 TPI from 2 3/8 in upward. So at 2 3/8 in, 2 7/8 in and 3 1/2 in the NU pin is 10 TPI and the EU box is 8 TPI — mechanically incompatible regardless of diameter. At 4 in and 4 1/2 in both forms are 8 TPI. The upset also changes the box OD: a 2 7/8 in NU coupling is cut on 2.875 in body while the EU box OD is 3.094 in.
What is the difference between API 5B and API 5CT?
API 5B specifies the threads themselves — form, taper, pitch, thread lengths, pitch diameters, makeup dimensions and the gauging practice used to verify them. API 5CT specifies the pipe: grades, chemistry, mechanical properties, dimensions, masses and which connections are available in which size and weight. A casing joint is therefore described by both documents at once: API 5CT gives the 9 5/8 in 47 lb/ft P110 body, API 5B gives the LTC or BTC thread cut on its ends. The two also serve different parties — 5CT governs what the mill produces, 5B governs what a threading shop and its gauges must achieve.
Which edition of API 5B do these tables come from?
The 16th Edition, dated December 2017, incorporating Errata 1 (2018), Errata 2 (2018) and Addendum 1 (2018). Every dimension on this page is read from that edition. Values are given in inches, which is how API 5B tabulates them — unlike API 5CT, which carries both SI and USC annexes. Buyers working in millimetres should convert from these inch values rather than from a secondary metric table, because rounding applied twice introduces error at the fourth decimal, which matters on pitch diameters.
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