This type of hard rubber wheel caster can be found on both Rock-ola and Seeburg models from the late 1950s until the 1970s. 

Before you decide to buy these casters PLEASE TAKE THE TIME to measure your caster and compare it to the measurements I will outline below and are shown on the card seen in the last two photos.      

I am calling the casters offered in this listing Type BR. 
This is a 2 inch diameter hard rubber wheel assembly with a base plate that measures 1.875 inches wide by 2.625 inches long.
 (The metric equivalents are 5.05 cm diameter by 4.76 cm wide by 6.68 cm long.)

The mounting hole dimensions are 1.375 inches on the short side and 2.125 inches on the long side, center to center.
(The metric equivalent here is 3.50 cm and 5.40 cm.)

They have not been cleaned - the ball bearings seem good and the wheels move freely.

I have divided this style of 2 inch diameter caster into four classes - type AS, type AR, type BS and type BR.

This listing is for type BR - if it does not match your needs please search my store for the other 3 types.