It looks to me like a 1" diameter ball. The maker, "REX-MATHEWS", appears to no longer be with us.
There's only the one, which renders this thing a bit useless.
Ball casters are something I have no experience with. I'm impressed by the smoothness of the ball's rolling action. I must keep this type of caster in mind for when I next need to put casters on something. Depending on the application, these could be a good way to go.
Meanwhile, I'll stash this in the box where I keep spare casters.
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While feeling the action of the ball in the caster, who should come to mind but Captain Queeg, the fictional American warship's captain in "The Caine Mutiny". [Go to 1:30 in the movie clip.] Captain Queeg would have been a ball caster aficionado for certain.
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