Can anyone identify what threads are used for the screws that hold the switch clusters together and the screws that fix the master cylinder onto the front of the block?
There seems to be two sized used on the twistgrip side to hold the switch together i.e. 32 TPI and 36 TPI. I want to replace the screws as some of the heads are getting chewed up and I want to get the correct size of screw so that I don't damage the aluminium body.
It looks to me like these threads have been re-tapped at some point.
Even when standard the thread sizes are a bit of a minefield and I've been wrong before!
http://www.oldbritts.com/nor_comm_72_18.html list the screws (Part No. 062241) as 10 x 24 2" which is a UNC size. So that's 24 tpi. These are the longer screws for the master cylinder to switch connection.
RGM Norton list the screw as 3/16" BSW which is also 24 tpi.
I reckon it's most likely that UNC threads would have been used originally here.
062488 is the shorter version of the screw for the clutch lever to switch side. 5/8" long and 10 x 24 tpi UNC.
If you want to use the threads that you currently have you'll need to try some different from standard size screws. Size 10 x 32 tpi is a UNF size. Perhaps a metric equivalent might be available for 36 tpi.
Phew! I'm out of time to look further.
Hope this helps.
RGM think that they are 3/16" Whitworth which is 24 TPI.
I think he's asking about an 850 Mk3. The big ones are M5 and the little one is M4.
Good stuff Stan.
That makes sense.
See post #16 and others here.
Sorry, forgot to say it is a 1976 Mk 3 Commando. I'll try M4 and M5 screws tomorrow.
Went out to check today and found that Stan is correct and M4 (0.7mm pitch) and M5 (0.8mm pitch) screws fit perfectly. That makes it very simple to replace them.
Thanks for your help.