My original caps would not screw on and I didn't want to grind on them. I got some new caps on ebay. They still needed trimming after the nubs were sanded off. Marked the ring with blue tape the sanded off about a 1/4 inch. After that was done they went on nice and tight.
http://i2.photobucket.com/albums/y10/allenlee/Silverado/50grit.jpg
http://i2.photobucket.com/albums/y10/allenlee/Silverado/4caps.jpg
http://i2.photobucket.com/albums/y10/allenlee/Silverado/likearock.jpg
http://i2.photobucket.com/albums/y10/allenlee/Silverado/duramax.jpg
http://i2.photobucket.com/albums/y10/allenlee/Silverado/pirelli.jpg