If you're trying to remove what might appear to be an adapter so the deep dish dual type wheels fit... I don't believe there is any adapter, just the one piece hub and the separate drum, probably held on with those 6 bolts you removed.

•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
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-