Custom Exhaust Question

[0m3nc0w]

I'm doing my first build on a '78 R100/7 and will be adding exhaust like this. Wondering if anyone can give me the outer measurement of the stock exhaust where I have the arrow.

Image of exhaust

Exhaust3.gif (97.79 KiB) Viewed 1016 times

Thanks!

[mattcfish]

38mm on most or 40mm for some of the big valve bikes.