The problem was extracting the remaining plastic bolt. A strong knife blade did the trick. A screwdriver blade might have worked. I drove the knife blade into the remaining threaded part in the dryer and twisted to extract the broken-off piece, then screwed in the replacement by hand. There is a plastic insert that fits into the bolt head which forms the contact surface with the floor. I removed this part form the old bolt head by prying with a small screwdriver then pressed it into place on the new part.