It's a cam lock, and most are 5/8" I believe. The cheapest way to get one would probably be to go to your local hardware store like Home Depot. They're actually overpriced, but when you factor in shipping from an online site, you're probably better off just getting it there. But if you need to get a bunch, want matching locks (1 key for all locks), or need to order other parts, Bob Roberts has them cheap.