Cleaning up an old auto rotisserie and found the casters attached by these neat brackets. I've never seen these before. They take a standard size 2 1/2 x 3 5/8 plate caster and hold in place with one cross bolt. Not sure why anyone would want option to change casters so assume they're mainly just for ease of attachment. Seems like I'm always futzing around bolting/welding casters on something but I may try to find some of these next time.