Home > How To > How to avoid cross threading new rubbers With the Euro rubbers the ends sometimes have quite a bit of rubber past the collars. This is usually the main cause for cross threading rubbers when we screw them in. The best is a bench grinder where we make them into a conical shape. Or with a pair of side cutters, trim around the edges. We don’t want to go too far as the swollen part of the rubber is there to stop them pulling through the collar.