A few days ago I needed to clamp something and none of my clamps were the right shape, so I went to the local hardware store and got one of these clamps. At the time I didn’t know what it was for — all I knew was that it was the right shape for me.
After I finished using it, I noticed that it had a model number on it, so I looked it up online to find out what it had been designed for. It turned out to be made to hold a pair of locking (Vise-Grip) pliers firmly to the edge of a table. I tried it out with my Vise-Grips, and sure enough, it was a perfect fit.
This is something I would have bought years ago and used all the time if I’d known it existed. Enclosed is a picture of it in action (something I couldn’t find online). I think just about anyone who uses Vise-Grip pliers regularly could use one of these.
[Update: A commenter pointed out that they are available for different sized locking-pliers.--OH]