who knows dobros?

[Quickstep192]

I've been shopping for dobro parts for a franken-banjo project I'm thinking about. I see a cover plate for spider bridge resonators on StewMac that says it's 11-3/32" diameter, but most of the others I see say they're 10-1/2". Is it possible that 10-1/2" refers to a nominal measurement (like maybe the size of the resonator it covers) and that StewMac is measuring the actual outside diameter?
Or, do these things really come in different sizes?

[John Arnold]

You've got it right. The cone for a spider bridge is 10 1/2" in diameter, nominally. That is the size of the recess that it fits in the guitar. The cover plate overlaps that, hence the larger diameter.
Biscuit cones and cover plates are about an inch smaller in diameter.