[markeb01]

In my experience the original 1966 six lug drum brake wheels only came with 3 hubcap retaining bumps. I never saw a 4 bump/nub wheel until sometime in the 1970's, when most of the hubcaps were being produced from aluminum.

Earlier stainless or chrome plated steel hubcaps will still fit on the 4 bump wheels, but careful installation is prudent or the earlier caps can split at the bead. Inspection of the wheels will show on 3 bump wheels, all three bumps are identical. On 4 bump wheels there are two "regular" sized bumps and two smaller bumps. These offer stronger retention than the earlier wheels, but can also cause a marginal hubcap to tear at the edge.