I bought two new front hubs for my 1994 Mustang and can't find replacement dust covers. The opening in the hub where the cap goes is 2.28 inches and the Ford replacement cap is 1.78 inches. My new hub is a National made by Federal Mogel. I checked 3 other hub manufactures and found the opening to be the same. Why can't I find a dust cap to fit? I screwed up and dumped the old hubs and dust caps before I bought the new, so I have nothing to compare to. Thanks for any help.