They're for circle burners, work great on a leaf spring car, makes for quick adjustments of pinion angle, spring height, etc. Also use clamp on brake caliper mounts, shock mounts, control arm mounts, etc. I've got an old set off the last leaf spring car we ran (probably 25 years ago) that I still use for mockup. Don't think I'd want them on the street, they don't slip near as much as you would think they do but they're not really a big enough base to properly locate the leaf spring for miles and miles of hassle free street service.....