I'll retract my statement about the small car caps being retro. I guess I was thinking about the full covers which are available at Danchuk and Classic Chevy Int. I have seen 54-55 car hub caps on the later wheels with the bumps. You probably have 60's wheels which have the 3 bumps and used a small cap. Truck Shop has the small caps for 62-64 trucks.
Fred

1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine