Too easy you always lose the suitable chuck-key ... (even if you install it on the power cord of the drill :-() had given the machine and the chuck key was gone. OK ... never bring your tool ... but I did it. ... Been short ... Spare used the exact size is not known ... ordered universal chuck Cross Key and not disappointed. is serving and has by its square hole in the middle is now a cord that hangs on the power cord of the drill.