ASME B16.5 Lap Joint Flange Dimension Lookup

Select a nominal pipe size and pressure class to read the key drilling dimensions for a lap joint backing flange. Because ASME B16.5 drilling is shared across flange types, these bolt circles also match your weld-neck and blind flanges at the same size and class.

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Source: ASME B16.5 — Pipe Flanges and Flanged Fittings (NPS 1/2–24, Class 150 and 300 carbon-steel lap joint pattern). 1 inch = 25.4 mm. Class 600 and above ship in the downloadable spec sheet.