I know you said in the first post it is not but that last description almost sounds like an RH-5° wheel, and if so then no real surprise it let go. Curious to see some pictures of it.

For reference this is what one looks like in cross section. https://picasaweb.google.com/lh/photo/96LV_PnM-bC97_4AoWK_G9MTjNZETYmyPJy0liipFm0?feat=directlink

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-