This set of casters with sockets came from the Rock-ola 1432 base seen in the last two photos.

This type of caster with a 2 inch smooth shank caster is normally found on Rock-ola models
STD-39 Standard, DE-39 DeLuxe, SUP-40 Super, MAS-40 Master, 1418 Commando, 1422, 1426, 1428, 1432, 1434 and perhaps both earlier and later models.
The caster shank is 7/16 of an inch in diameter and about 2 inches long.
The rubber tire is 2 inches in diameter and 1 inch wide or thick.
Please see the last two photos which I offer as a reference.

These work with sockets that have a circular brass spring inside which grips the shank.
There may be some surface rust.