I'd either make a plug or use a cycle thread part. Both imperial, 26tpi but a 60degree thread rather than 55degree. The difference won't matter in my book

Charles

I had reached the same conclusion and ordered some blanking plugs of that size, thank you all.

Sorry chaps,
but it is in fact a 1/8" BSP thread, in fact all the oil gallery cover threads are BSP.

Location: Deepest darkest Kent

I would have thought so too Robert. All the other oil plugs are BSP.
28 and 26 tpi are easy to confuse but Stuart Giles is chap who knows his engines....

No idea about the crankcase thread, but 3/8 x 26 BSB grubscrews are easily made from old bicycle wheel axles for those of us who lack the equipment/patience to screwcut them! W

For those interested 1/8" bsp plugs fit a treat - thank you all, on and off the Forum.

As pointed out to me, the small top gallery blanking plug also fits

Ruairidh,
What year was/is the crankcase you were working on? Can't remember the exact number on the one in my photo that I had to make the BSB ones for, but it had been a 1 1/8" crank case from the factory, and those holes were definitely too small to take a 1/8" BSP plug.

Just wondering if it is another A7 oddity like the numerous different sizes of front camshaft bush for no apparent reason.

Location: N W Kent

Hi Stuart,

I have used the 1/8" BSP in a 1924, 1932 and 1934 crankcase without issue in the last week. If I find anything different in future I will come back to this thread.