How interchangeable are B-port risers.

So we have B-port mills and many brands like Jet, Enco, no-name and known names.
Many appear to be copies or clones. Some appear very close but have more metal in some places. Some I think may have less metal.

But will a riser from one fit another without some "massaging" ?
A machine without a riser block is just about useless to me and I have always spent the long dollar and bought the matching one with the machine.
Perhaps money to be saved on e-yuck nowadays.

Are the clones that look alike the same dimensions or is there a metric/english difference?
Asking for been there done that.
I have wondered about if I was leaving money on the table or waiting for long deliveries with a machine on the floor that I can't efficiently use sometimes.
I've never measured them across the brands and models that I have owned which now that I think about it makes me......:dunce:
Bob