Cap Dimensions
A domed end closure welded onto the end of a run. E is measured from the welding end to the outside of the crown, so it is the length the cap adds to the pipe. It is the one B16.9 dimension on this site that depends on the wall thickness.
- Standard
- ASME B16.9
- Dimension
- Length E
- Size range
- NPS 1/2 – NPS 24
- Sizes published
- 21
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| Size | Matching pipe OD | Length E | Limiting wall thickness | Length above the limiting wall |
|---|---|---|---|---|
| NPS 1/2 | 0.840 in | 1.0025.40 mm | 0.184.57 mm | 1.0025.40 mm |
| NPS 3/4 | 1.050 in | 1.0025.40 mm | 0.153.81 mm | 1.0025.40 mm |
| NPS 1 | 1.315 in | 1.5038.10 mm | 0.184.57 mm | 1.5038.10 mm |
| NPS 1 1/4 | 1.660 in | 1.5038.10 mm | 0.194.83 mm | 1.5038.10 mm |
| NPS 1 1/2 | 1.900 in | 1.5038.10 mm | 0.205.08 mm | 1.5038.10 mm |
| NPS 2 | 2.375 in | 1.5038.10 mm | 0.225.59 mm | 1.7544.45 mm |
| NPS 2 1/2 | 2.875 in | 1.5038.10 mm | 0.287.11 mm | 2.0050.80 mm |
| NPS 3 | 3.500 in | 2.0050.80 mm | 0.307.62 mm | 2.5063.50 mm |
| NPS 3 1/2 | 4.000 in | 2.5063.50 mm | 0.328.13 mm | 3.0076.20 mm |
| NPS 4 | 4.500 in | 2.5063.50 mm | 0.348.64 mm | 3.0076.20 mm |
| NPS 5 | 5.563 in | 3.0076.20 mm | 0.389.65 mm | 3.5088.90 mm |
| NPS 6 | 6.625 in | 3.5088.90 mm | 0.4310.92 mm | 4.00101.60 mm |
| NPS 8 | 8.625 in | 4.00101.60 mm | 0.5012.70 mm | 5.00127.00 mm |
| NPS 10 | 10.750 in | 5.00127.00 mm | 0.5012.70 mm | 6.00152.40 mm |
| NPS 12 | 12.750 in | 6.00152.40 mm | 0.5012.70 mm | 7.00177.80 mm |
| NPS 14 | 14.000 in | 6.50165.10 mm | 0.5012.70 mm | 7.50190.50 mm |
| NPS 16 | 16.000 in | 7.00177.80 mm | 0.5012.70 mm | 8.00203.20 mm |
| NPS 18 | 18.000 in | 8.00203.20 mm | 0.5012.70 mm | 9.00228.60 mm |
| NPS 20 | 20.000 in | 9.00228.60 mm | 0.5012.70 mm | 10.00254.00 mm |
| NPS 22 | 22.000 in | 10.00254.00 mm | 0.5012.70 mm | 10.00254.00 mm |
| NPS 24 | 24.000 in | 10.50266.70 mm | 0.5012.70 mm | 12.00304.80 mm |
Length E applies where the wall of the cap is no thicker than the limiting wall thickness. Above it the longer length applies. Editions of B16.9 up to 2018 call the longer length E1.
Check the wall before dimensioning. A cap is the one buttweld fitting whose length depends on its wall thickness, so the schedule has to be known before the overall length of a capped spool can be fixed.
Not tabulated here. The length in the main table applies up to the limiting wall thickness for the size. A cap with a heavier wall is longer. Editions up to 2018 call the longer length E1; the 2024 edition calls both E.
Guides and comparisons for this page
Common questions
What is the length e of an NPS 8 buttweld cap?
4.00 in (101.6 mm). ASME B16.9 dimensions depend on NPS only, so this figure is the same in every schedule.
Does the buttweld cap dimension change with wall thickness?
Yes, for a cap. ASME B16.9 gives one length for walls up to a limiting thickness and a longer one for heavier walls. In NPS 6 the cap is 3.50 in long up to a 0.43 in wall and 4.00 in long above it. The cap is the exception: elbows, tees and reducers keep one dimension in every schedule.
What material are buttweld caps made from?
Carbon steel fittings are normally ASTM A234 WPB, matched to A106 Gr B pipe. Low-temperature service uses A420 WPL6, stainless uses A403 WP304/WP316, and chrome-moly uses A234 WP11, WP22 or WP91. See the material grade reference.