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[firenze]

Hi, this will be an obvious question for some but I'm not good on old thread sizes etc so this is the problem . I have a pre war tank with a oblong removable lid in the centre where the ammeter and switch live. It should be held in with 2 screws/ bolts which locate in threaded bosses . Does anyone know what thread they are likely to be so I can try and find replacements . I don't want to try random screws just in case I ruin the original threads!

[simon]

BA most likely if they are machine screws.

[MadMike]

Simon may be correct if the screws are particularly small. Remember that a 2BA thread is a mere 3/16 diameter. BA threads were mostly at that time used on electrical equipment. The chances are considering the age of the bike that the threads are BSCY, usually referred to as Cycle Threads. The Cycle Thread (see what I did there) up to 7/16 diameter has a constant thread pitch of 26 TPI (Threads Per Inch). Of course it is entirely possible bearing in mind the age of the bike that somebody has bodged a screw with a different thread into the original holes. If it is a cycle thread they are available from a number of suppliers, particularly at Stafford next week. HTH.

[PeteF]

Ebay is also good for odds and ends like this.
You should be able to measure the diameter of the screw (which will be in imperial of course) If it's not too small a hole you might get a rod with a bit of bluetack on it and measure the number of threads per inch. If you get that information then you're home and dry.

[MadMike]

On the other hand Pete, he could simply take out the existing bolt and measure that. LOL.

[PeteF]

I think he's lost the bolts Mike
"It should be held in with 2 screws/ bolts which locate in threaded bosses"

[firenze]

I met an old boy today with a tray full of screws bolts etc in his shed/ workshop all old pre metric I picked out a couple which do look like old brass electrical types to me , will soon know if they are correct. If not will shop for those suggested till I find them ! Thanks everyone for your help!

[PeteF]

Don't push it - some of the imperial threads are close but not close enough and it would be easy to strip the thread in the bosses.