I'm trying to size a bolt from a 1980s bike so I can get a replacement. It is the bolt which holds a downtube gear shift lever in place (screws into a band on shimano altus fitting). Its diameter over the threads is 4.3mm. This doesn't seem to map to either a whitworth or a BA thread, but I know it aint metric cos M4 is too small and M5 is too big.
Can anyone help?
Can anyone help?