Sears Employee: "I'm pretty sure they don't make that...and if they do, we don't sell 'em."
I previously wrote about gunsmithing/hollow-ground screwdriver bits here, and in the two years since, my ever-growing collection has served me well in my machine repair hobby. But a few months ago, as I diversified into larger industrial sewing machines, I began encountering huge screws I had no bits for. (If you have old woodworking machinery, factory machines or similar, you may have encountered the same thing when trying to repair or adjust them.) These screws had heads a half-inch or more in diameter, with slots in odd widths like 0.087"; the largest Brownells bit available is too small by half, in both dimensions.
Googling "Large hollow-ground screwdriver bits" yielded no results. Burning shoe leather didn't pay off either--three local hardware store clerks, two people in the Craftsman section of the local Sears and even a local gunsmith all had no idea where I could find extra-large hollow-ground bits. But finally an old-school mechanic in an online forum turned me on to what I was looking for: They're called "drag link sockets."
A "drag link" is an outdated piece of steering linkage found on utility vehicles like trucks and jeeps. And it's held on with a big-ass machine screw. "Drag link sockets" are therefore just huge hollow-ground bits with a female end that accepts the square drive of a socket wrench, to get the drag links off.
Once I had the appropriate term to Google, I found they're still made and sold by a lot of different manufacturers. Including, of course...Sears Craftsman. Anyways I've titled this post so that the next poor bastard replicating my initial search will find the answer right away.