Here's the mast cap made from a thick plastic chopping board.
It's cut to the size of the mast, then it's filed down to fit inside the mast with a lip on the top so it can't be pushed in. This stuff is quick and easy to work with compared to metal.


You can also see how a Ronstan pulley can be fitted to our masts with just a pin to hold it in place. No need to rivet it.