The Bearing Buddy prevents wheel bearing failure on boat, snowmobile, ATV, RV and utility trailers. It eliminates bearing repacking and keeps water and dirt out of hubs and bearings. Features stainless steel components, chrome plated steel barrel and is easy to install. You can choose to purchase your set with the Bearing Buddy bra which is a vinyl cover that fits over the Bearing Buddy to contain excess grease and keep it off tires and wheels. Properly installed and maintained, Bearing Buddy prevents wheel bearing failure and eliminates bearing repacking. Trailer wheels can be completely submerged. The automatic pressure relief feature allows excess grease to escape if the hub is overfilled. Measure the inside diameter of the hub or the outside diameter of the dust cap shoulder (the part that fits into the hub) with a caliper or micrometer. The measurement needs to be in thousandths of inches.