The Yankee screwdrivers took bits in three different diameters: 7/32", 9/32", and 5/16". The small and midsized drivers are pretty common, but the honkin' big drivers (#31 and #131) don't show up often. I've managed to acquire examples in all three sizes, but I don't use the big one much. I'd have to be doing production door installation or something like that for the big one to make sense.