Yes chromed steel. I only have one dustcap (if I have it) and won't be able to look till next week. I could send you a ND stronglight crank-arm but the diameter is 23.35 so not really a suitable candidate for the experiment. The steel is pretty thin though so there is a good chance it wont hold as other's have pointed out. You would probably need to fabricate a washer that is just the right size to fit under the cap, such that it is really wedged in there. Do you have self extracting bolts already?