Hi altan, I took mine apart last weekend. I do not know the key size, but it is smaller than I thought it would be. I just went into the crane test and turned the machine off mid-test so the hex key faced the inside of the cabinet. Then I could get my fat head in there to look at it. If you still need the hex key size I can look at my set and tell you later today. On a slightly different note, I could not get my crane adjusted properly. It drops the balls onto the disk as opposed to through the opto path like it's supposed to. Any insight you may have on how to adjust the crane position or magnet timing would be much appreciated.