I actually just purchased a 93 Ranger 2wd yesterday to use as a commuting vehicle for school (and to haul parts for my project car). Had a caliper seize and so I had to replace it (and the bearings) on the side of the road. However, I don't have that sheet metal nut (looks like a castle nut) or a dust cap on the passenger side, and the dust cap is missing on the driver side.

While I can easily acquire dust cups for a couple bucks, I can't seem to find that lock nut looking piece. Is there a particular name for the piece or an alternative method to secure it and keep the actual nut from backing off? I had thought perhaps getting a castle nut in the proper size and threading it on to use, or just getting a few regular nuts that are large enough to at least keep the nuts from backing too far off (imagine that may damage the cotter pin though if they try to back off.) Any suggestions?