those caps that were retained behind the wheel wouldn't work with a hubcentric wheel. they needed a bigger hole like an aftermarket chrome steel slot or some chrome reversed wheels had, or if your stock wheel was lugcentric. i remember the local "western auto" store had those caps in both versions next to the bins filled with chrome wheel nuts. i can't recall who made them though. my cousin had a '58 buick century with flat caps in the rear, cone caps in the front, chrome lugnuts, and chrome trim rings on black steel wheels with twin 3/8"[i think] whitewalls. the car was a bright gold and all the chrome work was very nice. that wheel/tire combo looked good on that car.