No idea if you have the original chuck for your lathe but still I wouldn't know the size. If you don't want to make one, measure what size you need & buy one. There are many places that sell replacement chuck keys assuming the pinion is not a hex or male square, those are harder find. Machining supply houses like MSC, KBC, Travers, etc. Mcmaster sells them too. Plenty to be found on ebay.