Metallic transfer from screwdriver to screw appears to adversely influence the corrosion resistance of the screw. A judicious balance between composition and hardness must be aimed at in selecting a suitable screwdriver. The composition of the driver must be related to that of the screw. Of the screwdrivers tested, one of AISI 420 stainless steel appears to be most suitable for both AISI 316 and cobalt-chromium-molybdenum screws. Its hardness of Rockwell-C 49 to 51 is hard enough for good wear but the driver should certainly be no harder than this if excessive mechanical damage to the screws is to be avoided. About Rockwell-C 40 would appear to be a happy compromise as far as screw corrosion goes.
One may speculate that a cobalt-chromium-molybdenum alloy screwdriver of greater hardness than the screws made of the same alloy might be the ideal one for handling these screws.
Further radioactive-isotopic experiments have been undertaken to determine the amount of metallic transfer between screwdrivers and screws of various alloys and will be reported shortly.