Rockwell Billet caps and billet carier bearing spanner nuts were designed after we took care of all the other weak links in the toploader. The gears and shafts would hold up but then blow the stock cast caps out. All billet 4140. tests have proven a major decrease in failures. Actually...none have been reported as of yet. Send us your chunk or we can provide one. This is a bulletproof system for big tires and horsepower.