In case you ever need to know.

So I'm out riding over the weekend. A friend of mine is using my board when he stops for no apparent reason. He tells us the mounting screw fell of the binding so his back foot came loose. I didn't have a spare and that was the only board out there. We had started pulling in the equipment to head home when the other guy on the boat with us tells us he fixed the board. Apparently, he used some thumb screw from the mountings for the long-since lost bimini top that originally came with the boat. If you're ever in the same situation, check your bimini for parts. We rode for another two hours off that makeshift solution. Then we hit a tree but that's a story I already covered in the boating section.

1/4 - 20 thread. Have a few extras available with a few washers. Buy SS allens and washers and throw in an allen wrench into a baggie. A squirt of WD-40 keeps the allen wrench from rusting.