Much of my work is indoors, and although the rubber feet on my 3221 generally work well, they can slip a bit when the legs start nearing full extension.
The round feet are just enough larger than 1” in diameter to prevent using 1” rubber furniture leg cups. Well, I subsequently came across some 1 1/8” ones made by Everbilt at Home Depot and snapped them up, even though they’re white. (“Well, I am a B&W photographer after all,” he rationalized.)
The photos show my solution. I used a matte knife to cut off the unneeded top portion (two inner embossed rings). Since the cup would not stay on, I cut a half-inch-wide rectangle from a 2” non-slip self-adhesive pad (same manufacturer) to insert, to take up just enough space to keep the cup secure but allow its easy removal, since I don’t always need it. I rinsed the powdery residue from inside the cups and dried them, and the rectangle adhered well.
Not the most elegant solution, but the traction is great.