Locknut size of C379 - 36090

Does anyone may be know what the size and tpi is from the locknut, securing the Ball-Pin of the rocker for valve adjustment ?
It’s for a 1938 Jaguar SS 2.5 engine.

C.379 is 5/16 x 26 British Standard Cycle (BSC or BSCY) thread. In case you are not familiar with this level of thread detail, it is not 5/16 x 22 British Standard Fine (BSF).

Hi Roger,
Thanks for the info and indeed BSF didn’t fit.

So you have DHC 36090? How about telling us some more, is it restored, or a project? What country are you in?

Hi Rob,
I’m afraid, 36090 is not the chassisnumber, it’s the partnumber of lock-nut C379.
Sorry for the confusion.

Ah, right, the Standard Motor Company part numbers.