Originally Posted by daleburr

I think if you use the kit plastic arm mount spacers they're probably okay.

But most racers use alloy spacers instead as the plastic spacers squash over time so aren't very accurate. The reduced surface area (therefore friction) of a small alloy spacer means that the mount/bushing assembly rotates around the screw.

If you read back through this thread there are lots of different solutions:

1. The dial-a-grip arm mounts with grub screws to lock onto the hingepins.
2. The Reflex Dynamics alloy spacers
3. Make some carbon fibre arm mount spacers.