These caps fit on a 3500lb truck trailer axle with Dexter hubs. The fit was very tight but perfect. Do yourself a favor, don't waste your money on a $28 driver installation tool. All you need is a 6-8" piece of 2" PVC for a DIY screwdriver. Put the cap in, wind it up and take it home. I used a large head rubber mallet to pound it almost all the way in and finally tapped the PVC driver with a 4 pound sledge turned sideways.