Borrani WM-0 x 21" Record 40 Hole Alloy Rim

I'm not sure why these rims are so much harder to find then the WM-1's but maybe they were too fragile under load? At any rate, the WM-0 stands for 1.40" versus the WM-1 which is generally a 1.60" (measurement is taken at underside of rim). Its kind of interesting with the terminology as the pristine one John Edwards is running on the panhead is labeled RM-0. I think his is actually an older rim. I may be wrong but think Borrani used larger lettering on the older rims and smaller letters on the newer ones. Does anyone know who made a WM-0 rim in steel as the only ones I've seen before are a couple of Borranis and a handful of Akronts, both obviously alloy?