Or, more to the point, where do I buy one?The small round part has a hole that slides over a motor shaft, and the big end is just plain flat, where you glue a sanding disk.
So far, I haven't been able to find one; this is probably because I don't know what to call it at google.
Of, if someone knows a supplier in the eastern LA county area (Whittier, Norwalk, Downey, etc.), don't hesitate to plug them! I'm designing a one-off disk sander on a stick, as it were, and getting all the parts from McMaster-Carr. They probably have a thing like the sketch (disk holder?), but I haven't found it yet, and I don't want to cost my client an arm and a leg whilst stumbling around in my ignorance, or worse, looking for the wrong thing! :-)
You can email me if you want, but please only as a cc of a post to the NG. To create an email, take the part of the url just after the tilde, and use the same domain. Put "SANDER WHEEL" somewhere in the subject line to stay out of the spam bin until I qualify your email. :-)