Lathe backplates??

[NJ Marty]

I cant figure these ones out and was wondering if they might be backplates for a lathe. They measure 3" across and seem to be made of brass or bronze.

 

[bmxdad]

They look like unfinished fuse caps. I've made something similar, but the unfinished side had rounded edges and a bolt pattern around the center hole.

 

[Packard V8]

All the lathe backplates I've seen were cast iron.

jack vines

 

[Matt Irvine]

Kind of look as tough they could be a blank for a bronze gear.