Lap Joint Stub End Dimensions
A stub end butt welds to the pipe and forms the lapped face that seals the joint. The lap joint flange slides on behind the lap and bolts through to the flange on the far side of the joint, not to the stub end itself. Only the stub end touches the process; the backing flange stays loose behind the lap and never sees the fluid.
Why the pair exists.
Because the backing flange is not wetted, it can be a cheaper material than the pipe. On stainless or alloy systems that is the whole point: a stainless stub end with a carbon steel backing flange gives the corrosion resistance where it matters, at a fraction of the cost of a solid alloy flange.
Bolt holes that swing.
The loose backing flange rotates freely until the joint is made up, so bolt holes can be aligned on site without rotating the pipe. On large-diameter and awkward field fit-ups that alone can justify the joint, which is why lap joints are common on tank nozzles and equipment connections that come apart regularly.
How To Read These Dimensions
The tables below are MSS SP-43 Type A, the long pattern, whose dimensions follow ASME B16.9. MSS SP-43 also defines a Type B short pattern and a Type C reducing pattern, and the overall length J differs between them. Confirm which type the spool was drawn around before ordering.
- T
- Wall and lap thicknessNominal wall at the welding end, which is also the thickness of the lap.
- K
- Lap diameterDiameter across the lapped face. It has to suit the backing flange sitting behind it.
- N
- Fillet radiusRadius at the back of the lap. The backing flange bears against this face, so its bore has to clear the radius.
- J
- Overall lengthWelding face to the face of the lap. This is the dimension that differs between the Type A long pattern and the Type B short pattern.
113 sizes across 6 schedules · dimensions in inches, weights in pounds · MSS SP-43 Type A
Schedule STD
| Nom. Pipe Size | Outside Dia. (Max.) | Outside Dia. (Min.) | Wall & Lap Thickness T | Lap Diameter K | Fillet Radius N | Overall Length (Long) J | Pipe Schedule Number | Approx. Weight in Pounds Lbs. |
|---|---|---|---|---|---|---|---|---|
| ½ | 0.896 | 0.809 | 0.109 | 1.38 | 0.12 | 3.00 | 40 | 0.30 |
| ¾ | 1.106 | 1.019 | 0.113 | 1.69 | 0.12 | 3.00 | 40 | 0.40 |
| 1 | 1.376 | 1.284 | 0.133 | 2.00 | 0.12 | 4.00 | 40 | 0.75 |
| 1¼ | 1.716 | 1.629 | 0.140 | 2.50 | 0.19 | 4.00 | 40 | 1.10 |
| 1½ | 1.965 | 1.869 | 0.145 | 2.88 | 0.25 | 4.00 | 40 | 1.25 |
| 2 | 2.456 | 2.344 | 0.154 | 3.62 | 0.31 | 6.00 | 40 | 2.25 |
| 2½ | 2.966 | 2.844 | 0.203 | 4.12 | 0.31 | 6.00 | 40 | 3.50 |
| 3 | 3.596 | 3.469 | 0.216 | 5.00 | 0.38 | 6.00 | 40 | 4.75 |
| 3½ | 4.096 | 3.969 | 0.226 | 5.50 | 0.38 | 6.00 | 40 | 6.00 |
| 4 | 4.593 | 4.469 | 0.237 | 6.19 | 0.44 | 6.00 | 40 | 7.25 |
| 5 | 5.683 | 5.532 | 0.258 | 7.31 | 0.44 | 8.00 | 40 | 12.00 |
| 6 | 6.743 | 6.594 | 0.280 | 8.50 | 0.50 | 8.00 | 40 | 16.00 |
| 8 | 8.743 | 8.594 | 0.322 | 10.62 | 0.50 | 8.00 | 40 | 23.00 |
| 10 | 10.913 | 10.719 | 0.365 | 12.75 | 0.50 | 10.00 | 40 | 36.00 |
| 12 | 12.913 | 12.719 | 0.375 | 15.00 | 0.50 | 10.00 | * | 47.00 |
| 14 | 14.170 | 13.969 | 0.375 | 16.25 | 0.50 | 12.00 | 30 | 35.40 |
| 16 | 16.180 | 15.969 | 0.375 | 18.50 | 0.50 | 12.00 | 30 | 44.80 |
| 18 | 18.190 | 17.969 | 0.375 | 21.00 | 0.50 | 12.00 | * | 57.20 |
| 20 | 20.240 | 19.969 | 0.375 | 23.00 | 0.50 | 12.00 | 20 | 71.00 |
| 24 | 24.240 | 23.969 | 0.375 | 27.25 | 0.50 | 12.00 | 20 | 102.00 |
Schedule XS
| Nom. Pipe Size | Outside Dia. (Max.) | Outside Dia. (Min.) | Wall & Lap Thickness T | Lap Diameter K | Fillet Radius N | Overall Length (Long) J | Pipe Schedule Number | Approx. Weight in Pounds Lbs. |
|---|---|---|---|---|---|---|---|---|
| ½ | 0.896 | 0.809 | 0.147 | 1.38 | 0.12 | 3.00 | 80 | 0.38 |
| ¾ | 1.106 | 1.019 | 0.154 | 1.69 | 0.12 | 3.00 | 80 | 0.51 |
| 1 | 1.376 | 1.284 | 0.179 | 2.00 | 0.12 | 4.00 | 80 | 1.00 |
| 1¼ | 1.716 | 1.629 | 0.191 | 2.50 | 0.19 | 4.00 | 80 | 1.25 |
| 1½ | 1.965 | 1.869 | 0.200 | 2.88 | 0.25 | 4.00 | 80 | 1.75 |
| 2 | 2.456 | 2.344 | 0.218 | 3.62 | 0.31 | 6.00 | 80 | 3.00 |
| 2½ | 2.966 | 2.844 | 0.276 | 4.12 | 0.31 | 6.00 | 80 | 4.50 |
| 3 | 3.596 | 3.469 | 0.300 | 5.00 | 0.38 | 6.00 | 80 | 6.50 |
| 3½ | 4.096 | 3.969 | 0.318 | 5.50 | 0.38 | 6.00 | 80 | 7.75 |
| 4 | 4.593 | 4.469 | 0.337 | 6.19 | 0.44 | 6.00 | 80 | 9.50 |
| 5 | 5.683 | 5.532 | 0.375 | 7.31 | 0.44 | 8.00 | 80 | 17.00 |
| 6 | 6.743 | 6.594 | 0.432 | 8.50 | 0.50 | 8.00 | 80 | 23.00 |
| 8 | 8.743 | 8.594 | 0.500 | 10.62 | 0.50 | 8.00 | 80 | 32.00 |
| 10 | 10.913 | 10.719 | 0.500 | 12.75 | 0.50 | 10.00 | 60 | 53.00 |
| 12 | 12.913 | 12.719 | 0.500 | 15.00 | 0.50 | 10.00 | * | 62.00 |
| 14 | 14.170 | 13.969 | 0.500 | 16.25 | 0.50 | 12.00 | * | 89.00 |
| 16 | 16.180 | 15.969 | 0.500 | 18.50 | 0.50 | 12.00 | 40 | 96.00 |
| 18 | 18.190 | 17.969 | 0.500 | 21.00 | 0.50 | 12.00 | * | 112.00 |
| 20 | 20.240 | 19.969 | 0.500 | 23.00 | 0.50 | 12.00 | 30 | 125.00 |
| 24 | 24.240 | 23.969 | 0.500 | 27.25 | 0.50 | 12.00 | * | 151.00 |
Schedule 40
| Nom. Pipe Size | Outside Dia. (Max.) | Outside Dia. (Min.) | Wall & Lap Thickness T | Lap Diameter K | Fillet Radius N | Overall Length (Long) J | Pipe Schedule Number | Approx. Weight in Pounds Lbs. |
|---|---|---|---|---|---|---|---|---|
| ½ | 0.896 | 0.809 | 0.109 | 1.38 | 0.12 | 3.00 | 40 | 0.30 |
| ¾ | 1.106 | 1.019 | 0.113 | 1.69 | 0.12 | 3.00 | 40 | 0.40 |
| 1 | 1.376 | 1.284 | 0.133 | 2.00 | 0.12 | 4.00 | 40 | 0.75 |
| 1¼ | 1.716 | 1.629 | 0.140 | 2.50 | 0.19 | 4.00 | 40 | 1.10 |
| 1½ | 1.965 | 1.869 | 0.145 | 2.88 | 0.25 | 4.00 | 40 | 1.25 |
| 2 | 2.456 | 2.344 | 0.154 | 3.62 | 0.31 | 6.00 | 40 | 2.25 |
| 2½ | 2.966 | 2.844 | 0.203 | 4.12 | 0.31 | 6.00 | 40 | 3.50 |
| 3 | 3.596 | 3.469 | 0.216 | 5.00 | 0.38 | 6.00 | 40 | 4.75 |
| 3½ | 4.096 | 3.969 | 0.226 | 5.50 | 0.38 | 6.00 | 40 | 6.00 |
| 4 | 4.593 | 4.469 | 0.237 | 6.19 | 0.44 | 6.00 | 40 | 7.25 |
| 5 | 5.683 | 5.532 | 0.258 | 7.31 | 0.44 | 8.00 | 40 | 12.00 |
| 6 | 6.743 | 6.594 | 0.280 | 8.50 | 0.50 | 8.00 | 40 | 16.00 |
| 8 | 8.743 | 8.594 | 0.322 | 10.62 | 0.50 | 8.00 | 40 | 23.00 |
| 10 | 10.913 | 10.719 | 0.365 | 12.75 | 0.50 | 10.00 | 40 | 36.00 |
| 12 | 12.913 | 12.719 | 0.406 | 15.00 | 0.50 | 10.00 | 40 | 52.00 |
| 14 | 14.170 | 13.969 | 0.438 | 16.25 | 0.50 | 12.00 | 40 | 73.00 |
| 16 | 16.180 | 15.969 | 0.500 | 18.50 | 0.50 | 12.00 | 40 | 97.00 |
| 18 | 18.190 | 17.969 | 0.562 | 21.00 | 0.50 | 12.00 | 40 | 126.00 |
| 20 | 20.240 | 19.969 | 0.594 | 23.00 | 0.50 | 12.00 | 40 | 147.00 |
| 24 | 24.240 | 23.969 | 0.688 | 27.25 | 0.50 | 12.00 | 40 | 205.00 |
Schedule 80
| Nom. Pipe Size | Outside Dia. (Max.) | Outside Dia. (Min.) | Wall & Lap Thickness T | Lap Diameter K | Fillet Radius N | Overall Length (Long) J | Pipe Schedule Number | Approx. Weight in Pounds Lbs. |
|---|---|---|---|---|---|---|---|---|
| ½ | 0.896 | 0.809 | 0.147 | 1.38 | 0.12 | 3.00 | 80 | 0.38 |
| ¾ | 1.106 | 1.019 | 0.154 | 1.69 | 0.12 | 3.00 | 80 | 0.51 |
| 1 | 1.376 | 1.284 | 0.179 | 2.00 | 0.12 | 4.00 | 80 | 1.00 |
| 1¼ | 1.716 | 1.629 | 0.191 | 2.50 | 0.19 | 4.00 | 80 | 1.25 |
| 1½ | 1.965 | 1.869 | 0.200 | 2.88 | 0.25 | 4.00 | 80 | 1.75 |
| 2 | 2.456 | 2.344 | 0.218 | 3.62 | 0.31 | 6.00 | 80 | 3.00 |
| 2½ | 2.966 | 2.844 | 0.276 | 4.12 | 0.31 | 6.00 | 80 | 4.50 |
| 3 | 3.596 | 3.469 | 0.300 | 5.00 | 0.38 | 6.00 | 80 | 6.50 |
| 3½ | 4.096 | 3.969 | 0.318 | 5.50 | 0.38 | 6.00 | 80 | 7.75 |
| 4 | 4.593 | 4.469 | 0.337 | 6.19 | 0.44 | 6.00 | 80 | 9.50 |
| 5 | 5.683 | 5.532 | 0.375 | 7.31 | 0.44 | 8.00 | 80 | 17.00 |
| 6 | 6.743 | 6.594 | 0.432 | 8.50 | 0.50 | 8.00 | 80 | 23.00 |
| 8 | 8.743 | 8.594 | 0.500 | 10.62 | 0.50 | 8.00 | 80 | 32.00 |
| 10 | 10.913 | 10.719 | 0.594 | 12.75 | 0.50 | 10.00 | 80 | 63.00 |
| 12 | 12.913 | 12.719 | 0.688 | 15.00 | 0.50 | 10.00 | 80 | 87.00 |
| 14 | 14.170 | 13.969 | 0.750 | 16.25 | 0.50 | 12.00 | 80 | 123.00 |
| 16 | 16.180 | 15.969 | 0.844 | 18.50 | 0.50 | 12.00 | 80 | 161.00 |
| 18 | 18.190 | 17.969 | 0.938 | 21.00 | 0.50 | 12.00 | 80 | 205.00 |
| 20 | 20.240 | 19.969 | 1.031 | 23.00 | 0.50 | 12.00 | 80 | 251.00 |
| 24 | 24.240 | 23.969 | 1.219 | 27.25 | 0.50 | 12.00 | 80 | 359.00 |
Schedule 160
| Nom. Pipe Size | Outside Dia. (Max.) | Outside Dia. (Min.) | Wall & Lap Thickness T | Lap Diameter K | Fillet Radius N | Overall Length (Long) J | Pipe Schedule Number | Approx. Weight in Pounds Lbs. |
|---|---|---|---|---|---|---|---|---|
| ½ | 0.896 | 0.809 | 0.188 | 1.38 | 0.12 | 3.00 | 160 | 0.75 |
| ¾ | 1.106 | 1.019 | 0.219 | 1.69 | 0.12 | 3.00 | 160 | 0.95 |
| 1 | 1.376 | 1.284 | 0.250 | 2.00 | 0.12 | 4.00 | 160 | 1.13 |
| 1¼ | 1.716 | 1.629 | 0.250 | 2.50 | 0.19 | 4.00 | 160 | 1.51 |
| 1½ | 1.965 | 1.869 | 0.281 | 2.88 | 0.25 | 4.00 | 160 | 2.02 |
| 2 | 2.456 | 2.344 | 0.344 | 3.62 | 0.31 | 6.00 | 160 | 4.51 |
| 2½ | 2.966 | 2.844 | 0.375 | 4.12 | 0.31 | 6.00 | 160 | 6.02 |
| 3 | 3.596 | 3.469 | 0.438 | 5.00 | 0.38 | 6.00 | 160 | 8.80 |
| 4 | 4.593 | 4.469 | 0.531 | 6.19 | 0.44 | 6.00 | 160 | 14.10 |
| 5 | 5.683 | 5.532 | 0.625 | 7.31 | 0.44 | 8.00 | 160 | 26.40 |
| 6 | 6.743 | 6.594 | 0.719 | 8.50 | 0.50 | 8.00 | 160 | 36.40 |
| 8 | 8.743 | 8.594 | 0.906 | 10.62 | 0.50 | 8.00 | 160 | 60.00 |
| 10 | 10.913 | 10.719 | 1.125 | 12.75 | 0.50 | 10.00 | 160 | 113.00 |
| 12 | 12.913 | 12.719 | 1.312 | 15.00 | 0.50 | 10.00 | 160 | 160.00 |
| 14 | 14.170 | 13.969 | 1.406 | 16.25 | 0.50 | 12.00 | 160 | 190.00 |
| 16 | 16.180 | 15.969 | 1.594 | 18.50 | 0.50 | 12.00 | 160 | 245.00 |
| 18 | 18.190 | 17.969 | 1.781 | 21.00 | 0.50 | 12.00 | 160 | 309.00 |
| 20 | 20.240 | 19.969 | 1.969 | 23.00 | 0.50 | 12.00 | 160 | 379.00 |
| 24 | 24.240 | 23.969 | 2.344 | 27.25 | 0.50 | 12.00 | 160 | 542.00 |
Schedule XXS
| Nom. Pipe Size | Outside Dia. (Max.) | Outside Dia. (Min.) | Wall & Lap Thickness T | Lap Diameter K | Fillet Radius N | Overall Length (Long) J | Pipe Schedule Number | Approx. Weight in Pounds Lbs. |
|---|---|---|---|---|---|---|---|---|
| ½ | 0.896 | 0.809 | 0.294 | 1.38 | 0.12 | 3.00 | * | 1.75 |
| ¾ | 1.106 | 1.019 | 0.308 | 1.69 | 0.12 | 3.00 | * | 2.50 |
| 1 | 1.376 | 1.284 | 0.358 | 2.00 | 0.12 | 4.00 | * | 4.00 |
| 1¼ | 1.716 | 1.629 | 0.382 | 2.50 | 0.19 | 4.00 | * | 6.25 |
| 1½ | 1.965 | 1.869 | 0.400 | 2.88 | 0.25 | 4.00 | * | 6.50 |
| 2 | 2.456 | 2.344 | 0.436 | 3.62 | 0.31 | 6.00 | * | 9.00 |
| 2½ | 2.966 | 2.844 | 0.552 | 4.12 | 0.31 | 6.00 | * | 14.00 |
| 3 | 3.596 | 3.469 | 0.600 | 5.00 | 0.38 | 6.00 | * | 18.50 |
| 4 | 4.593 | 4.469 | 0.674 | 6.19 | 0.44 | 6.00 | * | 27.50 |
| 5 | 5.683 | 5.532 | 0.750 | 7.31 | 0.44 | 8.00 | * | 39.00 |
| 6 | 6.743 | 6.594 | 0.864 | 8.50 | 0.50 | 8.00 | * | 54.00 |
| 8 | 8.743 | 8.594 | 0.875 | 10.62 | 0.50 | 8.00 | * | 73.00 |
| 10 | 10.913 | 10.719 | 1.000 | 12.75 | 0.50 | 10.00 | 140 | 116.00 |
| 12 | 12.913 | 12.719 | 1.000 | 15.00 | 0.50 | 10.00 | 120 | 167.00 |
Materials We Supply
Lap Joint Stub End to MSS SP-43 Type A in the grades below. Tell us the service and we will confirm the right one.
| Material | Specification | Typical Service |
|---|---|---|
| Carbon Steel | ASTM A234 WPB / WPC | General process, steam, oil and gas gathering and utility lines |
| Low-Temp Carbon Steel | ASTM A420 WPL6 | Cold service to −50°F; LNG and northern pipeline work |
| Chrome-Moly Alloy | ASTM A234 WP11 / WP22 / WP91 | Elevated temperature; refinery heaters, power plant steam |
| Stainless Steel | ASTM A403 WP304/304L, WP316/316L | Corrosive service, chemical, food and beverage, water treatment |
| Duplex & Super Duplex | ASTM A815 UNS S31803 / S32750 | Chloride and seawater service, offshore, desalination |
Common Questions
What is a lap joint stub end?
A short butt weld fitting with a lapped face. It welds to the pipe and forms the sealing face, while a separate lap joint backing flange slides on behind the lap and carries the bolting through to the mating flange. The flange bears on the back of the lap rather than fastening to the stub end. Only the stub end contacts the process fluid.
Why use a stub end and backing flange instead of a weld neck flange?
Cost and alignment. The backing flange never touches the fluid, so it can be carbon steel behind a stainless or alloy stub end. It also rotates freely, so bolt holes line up on site without turning the pipe.
What is the difference between long and short pattern stub ends?
Overall length J, and the standard that defines it. The tables above are MSS SP-43 Type A, the long pattern, dimensioned to follow ASME B16.9. Type B is the short pattern and Type C is a reducing pattern, both shorter. Confirm which type the spool was drawn around before ordering, because they are not interchangeable in a fixed spool.
