The 3/8"-drive socket will now fit in the notch and on the nut, I'm happy to report. It took a while to grind it down enough, and it wasn't easy. As I said, the steel is tough. Tough enough that an old drill bit I had wasn't up to the task of drilling out the hole for the screwdriver to go through. I'm going to knock off for tonight and hit it with a new bit tomorrow. In the meantime, here's my grinder setup. Note the quarter-inch high pile of steel particles on the paper towel. Needless to say, I wore a mask, nitrile gloves, and eye protection. The bottom photo is a comparison with the 1/4"-drive socket.
NOTE TO SELF: Get a bench grinder, for God's sake. This would have been the perfect application for one.
