I got the final pieces for your viewing pleasure! This was a successful experiment on doing these at home! Without a machine called a Terret Lathe it is a bit more involved and they have a little bit more of that DIY air about them, but they are quite attractive and passed all the tests from my QA/QC department (my Uncles lips blowing through them). Good times!
I did two styles of the valve. A flat top valve if the builder wants to countersink the whole valve into his watercraft so it is flush with the surface and a valve with a radius (rounded top edge) for the builder who wants to place the valve slightly above the surface of the fiber-glassed board.
The leash-plug is just this one style in this batch, but I am going to design one with the lip a wee bit higher so it can be mounted from underneath a 1/4" board and be flush. These can be mounted that way, just a spacer of sorts needs to be placed on the valve or the board somehow, which is relatively easy. Or these can be mounted by boring a hole through the top like they have been in the past.
Check them out!