Article
Piping designers lay out lines using fitting dimensions from ASME B16.9. If a fitting is a few millimetres off, spools do not fit and site welding gets difficult. Understanding the main dimensions helps buyers check drawings and inspect deliveries.
The key dimensions
| Symbol | Fitting | What it measures |
|---|---|---|
| A | 90° LR elbow | Centre to end |
| B | 45° LR elbow | Centre to end |
| O / K | 180° return | Centre to centre / back to face |
| C / M | Tee and cross | Centre to end of run (C) and branch (M) |
| H | Reducer | End to end |
| E / E1 | Cap | Overall length (E1 for heavier walls) |
Example values for common sizes
| Size | OD (mm) | 90° LR (A), mm | 45° LR (B), mm | Tee (C), mm |
|---|---|---|---|---|
| 1" | 33.4 | 38 | 22 | 38 |
| 2" | 60.3 | 76 | 35 | 64 |
| 4" | 114.3 | 152 | 64 | 105 |
| 6" | 168.3 | 229 | 95 | 143 |
| 8" | 219.1 | 305 | 127 | 178 |
A useful rule: for sizes 3/4" and above, the 90° LR centre-to-end is 1.5 times the nominal size in inches, converted to millimetres.
Tolerances that matter
- Outside diameter at the bevel – must match the pipe within tight limits so that the weld root lines up.
- Inside diameter at the end – controls the step inside the joint.
- Centre-to-end – typically ±2 mm for smaller sizes, increasing with size.
- Off-angle and off-plane – the ends must be square to the centre-lines so the line does not run out of true.
- Wall thickness – not less than 87.5% of the nominal wall at any point.
Bevel ends
Unless otherwise ordered, B16.9 fittings are supplied with weld bevels to ASME B16.25: a 37.5° bevel with a 1.6 mm root face for walls up to about 22 mm, and a compound bevel for heavier walls.
Inspection tip
When checking a delivery, measure a sample of each size for centre-to-end, bevel angle, root face and wall thickness at the ends and at the extrados of elbows, where forming thins the wall most.
Frequently asked questions
What is the centre-to-end dimension of a 4" 90° LR elbow?
152 mm (6 inches) under ASME B16.9.
What is the minimum wall thickness allowed on a B16.9 fitting?
Not less than 87.5% of the nominal wall thickness at any point.
What bevel is standard on buttweld fittings?
A 37.5° bevel with about 1.6 mm root face per ASME B16.25, with a compound bevel for heavier walls.
Key takeaways
- Learn the symbols: A, B, C, M, H and E.
- 90° LR centre-to-end ≈ 1.5 × NPS.
- Check OD, bevel, root face and wall thickness on delivery.
Need these products?
Sawariya Metal Industries supplies stainless steel pipes, flanges and buttweld pipe fittings from Mumbai to buyers in India and overseas. Send your size, grade, standard and quantity through our enquiry form and we will reply with a clear quotation and the test documents you need. You can also browse our stainless steel pipes, flanges and buttweld fittings.