I am remounting some of the hardware and adding new hardware.

I noticed that there are nuts on the underside that have the washer built in and it is closed like an acorn nut. I can not find the name of what these are and where to buy. Any suggestions?

Also, I have to put some lewmar track on for the adjustable genoa cars. What have others used? #10 square bolts, etcs.

Thanks, Don