The inner race protrudes slightly beyond the shield so the metal spacer between bearings is not a problem. The nylon spacer normally should not be a problem, but the surface of some of the larger diameter spacers is cupped slightly or has mold flash. I think this is due to shrinkage after molding. Some people have reported that when the larger diameter spacers are tightened very tight, the inner race can cut into the the spacer. That, along with the cupped surface, can allow a little rubbing of the spacer on the shield. I have not seen/heard that on the 0.312 spacer. I am looking for a low cost metal spacer in the less than $0.25 range at a 1000 piece order.
"If you didn't build it, you will never own it."