I had a hard time finding this information, so I thought I would post it for other users. I lost the cam key after tearing the engine apart. When I started going back together(several months later), none of the local parts store had what I needed. I did find a post about tractor supply having the correct key. Anyway, I tore the front of a magnum engine at the local u pull it to get cam bolt and key then swung by the tsc. If you need just the key, the cheapest and quickest option is a 3/16" x 5/8" woodruff key from tractor supply.