Ed,

OSH stands for Orchard Supply Hardware. They have a good selection of nylon washers usually. I believe they are usually sold in 4 packs, but I don't have the part number or any other information at this time. The outside diameter is close in size to that of the thrust washer, the inside is somewhat larger, I just tack glue the nylon washer to the thrust washer with a couple drops of medium CA to keep it centered. Once the backplate, prop, and prop washer/nuts are installed it will hold just fine. I have attached a picture as well. I hope this helps.

Jim Smith