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Lap Joint Stub End Type A / B / C Selector
The most expensive mistake on a lap joint assembly is matching the wrong stub-end type to the backing flange — the difference is the fillet radius at the lap, not just length. Answer three questions to identify the correct type and dimensional pattern.
Recommended Standard
Type A Stub End
ASME B16.9 — long pattern
Large corner radius
Fillet / corner radius
Seats inside the lap joint flange bore
How it seats
+1.52 / -0 mm
Lap thickness tolerance
Type A is the stub end for a true lap joint (loose) flange. Its large fillet radius lets the lap seat cleanly inside the bore of the backing ring, giving full gasket bearing once machined.
Send your flange detail and pipe schedule for a stub-end match →
Source: ASME B16.9 (long pattern) and MSS SP-43 (short, light-wall pattern); lap thickness tolerance +1.52 mm / -0 (never thinner than nominal pipe wall). Type A/B/C corner-radius definitions per published standards.
