I will now describe a stroke of towering genius that came to me recently while replacing a bottom bracket cartridge. I expect I will soon learn that it's a trick that everyone else here already knew, and is considered to be so obvious that it scarcely bears mentioning. Ah, well.
When removing an old cartridge bottom bracket, or installing a French- or Italian-threaded one--either of which has to be
really tight to keep from working loose--I have always struggled, usually successfully, to keep the splined BB tool pressed tightly enough against the splines that it doesn't slip and damage them. I hate it when that happens.
The other day, it occurred to me to insert an M8 bolt in the square hole in the top of my Park BB2 bottom bracket tool--which ordinarily accepts a 3/8" drive ratchet--and thread the bolt into the spindle of the cartridge BB, making the dreaded slippage impossible. I used a 35 mm bolt, which was a good length for the long triple-crank cartridge I was removing. A 40mm might be better for a short double cartridge. It only has to be screwed in finger tight to keep the tool in place. Cranking the bolt down wouldn't hold it any better, but would probably damage the seals on the cartridge. I put a washer under the head of bolt before screwing it in, but I forgot to include it in the photos below.
Of course, you can't use a ratchet with the tool now, but that doesn't matter--you just grab onto the wrench flats with a big adjustable. I see from the Park catalog that my BB2 is apparently no longer in production, but the current model, the BB22, looks pretty similar. The same approach would work, I imagine, although it might require a longer or shorter bolt than the one I used.
That's it. I hope this is news to someone.