Stub End Dimensions: Long & Short Pattern Stub End Chart (ASME B16.9-2024)

1. What is a lap-joint stub end?

A lap-joint stub end is a short wrought butt-welding fitting. One end is a plain barrel, bevelled and butt-welded to the pipe; the other end is a formed or machined lap whose front face becomes the gasket seating surface. A loose lap-joint (backing) flange slides over the barrel and clamps the lap against the mating joint when the bolts are tightened.

Because the flange never touches the process fluid, it can be ordinary carbon steel even when the pipe and stub end are stainless, duplex or nickel alloy – a real saving on large alloy systems. The flange also rotates freely, so bolt holes line up with equipment nozzles without forcing the pipe. Stub ends belong to the same ASME B16.9 family as elbows, tees, reducers and return bends; see our overview of types of pipe fittings for where they fit in a piping system.

When to use a stub end – and when not to

• Good fit: stainless, duplex or nickel-alloy lines; systems dismantled often for cleaning or inspection; tie-ins where bolt-hole orientation is uncertain.
• Use with care: lines with high bending loads, vibration or thermal cycling – a lap joint has lower fatigue strength than a weld neck flange.
• Avoid without engineering review: severe cyclic service and high-class joints where the piping code or project specification calls for weld neck flanges.

2. Stub end nomenclature: G, F, T, R, OD and t

ASME B16.9 uses a small set of letters for stub ends. Using the same letters on drawings, inspection reports and purchase orders removes most dimensional disputes with suppliers.

3. ASME B16.9 stub end dimensions chart (NPS ½–24)

The chart lists every lap-joint stub end size in ASME B16.9-2024. Switch between millimetres and inches, type a size to highlight its row, or download the full chart as CSV. The pipe OD column (from ASME B36.10M / B36.19M, see our pipe sizes and schedule chart) is included so you can see how the barrel limits bracket the mating pipe.

4. Long pattern vs short pattern stub ends

Both patterns share the same lap diameter, fillet radius and barrel OD limits – only the overall length F changes. The choice is driven by flange thickness, weld access and cost.

5. Stub end types, standards and materials

MSS SP-43 stub ends are intended for light-wall stainless systems in low-pressure, corrosion-resistant service; they are not a substitute for B16.9 fittings in pressure-designed lines unless the design basis allows it. Fabricated laps (a ring welded to the pipe) are a code construction, not a catalogue item – confirm the governing code and project specification permit them before use.

Common stub end materials

The backing flange is usually ASTM A105 carbon steel (ASTM A350 LF2 for low temperature). Check galvanic and temperature compatibility, especially in coastal plants where a carbon-steel flange sits against a stainless lap, and size the bolting with a proper bolt torque and flange joint calculation.

6. Stub end tolerances (ASME B16.9)

The table isolates what applies to a stub end: the general welding-end tolerances plus the stub-end limits on G, R and T. Tolerances are equal plus and minus unless shown otherwise. The unit switch above also changes this table.

7. Stub End Selector & Acceptance Checker

Pick a size, pattern and wall basis to get every nominal value and acceptance limit in one place. Enter measured readings for an instant accept/reject per dimension, then print the result as a branded inspection record.

8. Stub end inspection procedure (step by step)

This sequence follows the general receiving checks in our pipe fittings inspection guide, with the stub-end-specific checks added.

1. Documents first. Compare the fitting against the PO: NPS, wall/schedule, long or short pattern, material grade and class, standard and edition, end preparation and the heat number on the mill test certificate (EN 10204 3.1 or as specified).
2. Marking and traceability. Confirm the manufacturer’s mark, material grade, schedule/wall, size and heat code are legible and match the MTC.
3. Visual check. Inspect the gasket face, fillet, barrel and bevel for laps, cracks, laminations, dents, pits and handling damage. The gasket face must carry the B16.5 raised-face finish (typically serrated) with no radial scratches.
4. Barrel OD. Measure with a calibrated micrometer or π-tape at two orientations 90° apart and check against the barrel OD max/min limits.
5. Lap diameter G. Measure across the lap in at least two orientations. Accept only between G minus tolerance and G – an oversize lap interferes with gasket centring inside the bolts.
6. Overall length F. Measure lap face to welding end at four points around the fitting; accept within ±2 mm of the ordered pattern length.
7. Lap thickness T. Measure at four locations away from the edge chamfer; every reading must be at least the nominal pipe wall.
8. Fillet radius R. Check with a radius gauge or profile template. R must not exceed nominal, otherwise the lap-joint flange will not sit flat on the lap.
9. Wall thickness and bore. UT-gauge the barrel; the minimum reading must be at least 87.5 % of nominal. Check ID at the end against OD − 2t ± tolerance.
10. Angularity. Check off-angle Q (lap face square to the barrel axis) and off-plane P with a square and feeler gauges or on a surface plate.
11. Weld bevel. For walls over 3 mm and up to 22 mm, verify a 37.5° ± 2.5° bevel and 1.6 ± 0.8 mm root face per ASME B16.25 (or the preparation required by the WPS); walls of 3 mm and less may be square-cut or slightly chamfered.
12. Flange trial fit. Slide the lap-joint flange on: it must rotate freely, seat fully against the back of the lap and leave the butt weld uncovered.
13. Record and disposition. Log nominal values, readings, instruments and calibration IDs, heat number, inspector, date and accept/reject. The checker above prints a ready-made record.

9. How to specify a stub end on a purchase order

A complete description prevents the most common supply errors. Give the data in this order:

Stub end, lap joint, LONG pattern, NPS 4 (DN 100), Sch 40S,
ASTM A403 WP316L-S, ASME B16.9-2024, ends bevelled to ASME B16.25,
gasket face to ASME B16.5 RF finish, MTC to EN 10204 3.1.

For an MSS SP-43 light-wall item, replace the standard with MSS SP-43 Type A, use class CR (for example ASTM A403 CR316L) and state the schedule (Sch 10S). Add the matching backing flange as a separate line item – for example “Flange, lap joint, Class 150, NPS 4, ASTM A105, ASME B16.5-2025”.

10. Common stub end mistakes to avoid

• Reading the OD columns of copied charts the wrong way round – many web tables label 22.8 mm as “min” and 20.5 mm as “max” for NPS ½.
• Applying the cap length tolerance (±3 / ±6 mm) to stub ends. The B16.9 length tolerance for stub ends is ±2 mm.
• Accepting a lap that is larger than nominal G, or a fillet larger than nominal R. Both tolerances are +0 – any oversize is a reject.
• Ordering “stub end, NPS 4” without the pattern, schedule, material class and end preparation.
• Pairing a short-pattern stub end with a thick Class 600 or 900 flange so the flange sits over the butt weld.
• Using a slip-on flange as backing for a Type A stub end (or a lap-joint flange on Type B) without checking bore and corner radius.
• Ignoring the gasket-face finish: the lap is the sealing face, so a scratched or unserrated lap will leak whatever its dimensions.
• Treating MSS SP-43 light-wall stub ends as interchangeable with B16.9 fittings for pressure design.

11. Test your knowledge: stub end dimensions quiz

Fifteen quick questions on ASME B16.9-2024 stub end dimensions, long and short pattern, tolerances, MSS SP-43 types, materials and inspection. Pick an answer to see the explanation straight away; your score updates as you go.

12. Frequently asked questions

13. Summary

A stub end is accepted on six numbers – barrel OD, G, F, T, R and wall – plus angularity, bevel and face finish. Take nominal values from ASME B16.9-2024, apply the stub-end tolerances (G and R plus-zero, T minus-zero, F ±2 mm), confirm the pattern and the weld clearance behind the flange, and record every reading. The selector above does the arithmetic and prints the record for you. Ready to test yourself? Try the stub end dimensions quiz above.

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References

• ASME B16.9-2024, Factory-Made Wrought Buttwelding Fittings (published 16 October 2024) – stub end dimensions, tolerances and notes.
• ASME B16.5-2025, Pipe Flanges and Flanged Fittings: NPS ½ through NPS 24 – lap-joint flange dimensions, raised-face diameters and facing finish.
• ASME B16.25-2022, Buttwelding Ends – weld bevel and root face geometry.
• MSS SP-43, Wrought and Fabricated Butt-Welding Fittings for Low Pressure, Corrosion Resistant Applications – Type A and Type B stub ends.
• ASME B31.3-2024, Process Piping – fabricated and flared laps and flanged joints.
• ASME B36.10M and ASME B36.19M – welded/seamless and stainless steel pipe dimensions and schedules.
• ASTM A234/A234M, A403/A403M, A420/A420M, A815/A815M and B366 – wrought fitting material specifications.