What size PVC cap? That is a cool idea.
They are caps for 3/4" Schedule 40 PVC pipe, so about 1 1/16" across the recess.
I had to look around a bit to find caps that were rounded on the end - easier to wrap the epoxy and glass around than the square-ended ones.
The cross bar is 3/16 SS rod which protrudes about 1/4" out each side of the cap, under deck.
I made a drill press jig for drilling the cross holes, and another for slicing off the excess cap depth on the bandsaw.
The only 'problem' is that even when the inside edge is rounded off, it is easy to abrade away the paint where a line exits on to the deck. I don't think it will be a problem in actual use, but I was pulling deck line through a bit too enthusiastically at one point when I was doing the rigging and there's now a bit of white PVC showing in one recess....inevitably in a spot that I can see from the cockpit, but that nobody else seems to notice!