Hello All,
Does somebody knows if there is a LIST with all types and sizes of the bolts, nuts and screws for the BSA m20.
I like to know the number of the part with length and TPI and which type of threat.
I found only a list in the part manual of 1939 with number and size and length, but no TPI or type of threat.
Richard 
email (option): bsa-m20@libero.it
I want to restore my BSA m20 and I think that the bike allready was restored before on a wrong way.
The bolts are on e diferent place as before, so I am not sure it's the wright size, but I found this list in the partlist of 1939 and maybe this will help.
But I think that not all of it does have CEI 26TPI.
Richard
email (option): bsa-m20@libero.it
Into aluminium at 1/4" and 5/16 diameters the threads are generally Whitworth...In larger sizes some are different (the cam follower guides for example)
Carburettors, switches, other electrical equipment, speedos and handle bar controls are mainly BA.(British Association)..
CEI (Cycle Engineers Institute/[BSCY] British Standard Cycle Thread) is also used in the 20 threads per inch form for some applications such as the rear wheel spindle, some frame bolts, barrel base studs etc. etc....Anywhere you find 20 tpi it will be this thread...
Headbolts and the oil unions into the crankcase are BSF.(British Standard Fine)...
Whitworth, CEI/BSCY and BSF all use the Whitworth head sizes on bolts but those sizes vary for a given diameter of thread in the different thread forms...
There is no definitive list of all the fasteners for any BSA M20/21 production year that I know of to date...
My advice would be to get some Imperial thread pitch gauges and the relevant thread form information...It's all on the internet...You will have to work out lengths etc. as you go if you can't find them in the manuals.....Ian
email (option): ian@wright52.plus.com