Following on from a previous post. It's not my digital calliper that's out.... It's the switches I was measuring. One batch of switches I have aren't quite M7 and aren't quite M6.... The threads are so poorly cut that at best they only just hold in a perfect cut M7 or drop out. Just.
I'll have to order another batch and there's no guarantee these will be any better. The fist batch I have are a perfect fit. It's a pleasure to screw them into the test barrel I just made. Will search my email and see who I got the good batch from.