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[Graham43]

Help please I have an Ewarts fuel tap with the lower part (fuel line to carb) being 3/8" x 20 tpi, and on the tank I need two 90 degree elbow fittings also 3/8" X 20 tpi, On the parts catalogue for similar fittings I see 1/4" or 1/8 gas - what do these fit?

[Presto]

Petrol Tap Thread Sizes are usually quoted in an odd size known as BSP or ‘Gas’. The thread size of calculated by taking the OD of the thread in inches and subtracting ¼ inch. This gives the following sizes: ⅛ GAS = 28tpi x 0.383 ins [3/8 approx]; ¼ GAS = 19tpi x 0.518 ins [1/2 approx]; ⅜ GAS = 19tpi x 0.656 ins [21/32 or 5/8 approx].