These are so cool, we had a Bigfoot camper and getting it just right to center it on the truck was a royal pain! My husband made these roller plates out of 1/4 inch steel with 6” wheels to put under the legs of the camper and we could roll the camper off and on the truck. The rollers worked great and there was no more yelling either.😁We have a set of 4. You must have a cement floor!! We no longer have a camper.