These came in the Patternmaker's Mother Lode, which makes a lot of sense, as clamping up awkward shapes such as wooden patterns is something they're apparently rather good at. And just as soon as I need to do that, I'll be ready and waiting. As Brian pointed out in the comments, Lee Valley still sells them, and their blurb explains their use as well as anything if you're not familiar with this particular breed of canine.
Anyway, it's a blessing to the tool accumulator when something is classed as a clamp. Why? Because we all know you can never have enough of those... ;)