Motorcycle wheels - rims are drilled at angles to fit specific hub dimensions. If you get a used rim and it is not matched to your existing hub, lacing it results in a nipple that does not line up with the spoke. It's sometimes possible to re-drill the holes at the correct angle and use larger nipples, but that takes maths, new parts, and no mistakes. I'm hoping for a simpler solution.
The nipple seats are in dimples. A curved washer inserted between the nipple head and the seat would allow some change of alignment - problem fixed.
I could make a simple press and get some flat washers and make 'em, but there are quite a few wheels in my garage to be laced, and there probably would be a small but steady market for such washers.
I've googled under "spherical washer", "motorcycle nipple washer", "seating washer" and a number of other terms, but nothing that looks right shows up. What I need is a normal flat washer that has been bent into a curve; a couple of hundred of them, actually.