British Standard Brass

A specialist thread form based upon the Whitworth thread and consisting of 26 threads per inch whatever the thread diameter.

The fixed TPI is based on the fact that brass tubing the wall thickness of brass tubing is independent of the diameter of the tube. This means that the thread depth must be the same whatever the thread diameter.

British Standard Brass
SizeDiameter [mm]Tapping Drill [mm]
BSB 1/8"3.1751.923
BSB 1/4"5.5565.098
BSB 3/8"9.5258.273
BSB 1/2"12.70011.448
BSB 5/8"15.87514.369
BSB 3/4"19.05017.798
BSB 7/8"22.22520.973
BSB 1"25.40024.148
BSB 1 1/8"28.57527.323
BSB 1 1/4"31.75030.498
BSB 1 1/2"38.10036.848

Note: All threads are 26 TPI [0.977mm].


See also: British Standard Whitworth, Thread.

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Subjects: Mechanical Engineering