If you are looking to put the keys on it, I used one like

these

for years. The ones I have are all brass and fully threaded. I don't recall them ever coming unscrewed. At the time I got them from the Coleman outlet store. A cheap model with interrupted threads (2 smooth flat sides & 2 radiused threaded sides) was constantly coming loose.

Edit to add:

P.S. Thanks for the reminder. I'm going to see if I've got any left and switch back.