My chain case screws were worn, some stripped, some about strip. I decided to replace them. BSA part No 1-4606 is a 2BA x 7/16" set screw, 16 required.
I don't know how easy it is to get 2BA screws in first world countries, but I tried my regular suppliers of imperial fasteners in Johannesburg without success. Someone suggested that 3/16 BSF screws are a close enough replacement. I tried to source these and only my least favourite supplier who charges 1000% could supply, but only 12. After scratching my head, I looked at the sizes:
2BA: 0.1850 OD x 31.3 tpi x 47 deg
3/16 BSF: 0.1875 OD x 32 tpi x 55 deg
5mm: 0.1969 OD x 31.75 tpi x 60 deg
Since the nuts were also probably worn, I ran a 5mm tap through the nuts, removing hardly any material but renewing the threads. I then fitted 5mm screws that I could buy anywhere.
This may horrify the purists but it works.
Original size is 3/16 cycle, 32 tip. The nearest size is AF,10x32. The angle is the only difference. Don't know why the American's used 10 instead of 3/16 but they did just to confuse us.
