This replacement Trailer Oil Cap is designed for 3,500lb Rated Dexter Brand Axles with Turbo Lube 5 Lug Hubs by Tie Down Engineering. These Hubs use Oil instead of Grease for their bearing lubrication method. The Oil Cap includes a new O-Ring, Plug, and the Cap itself. The Black Plastic Cap gives a clean look to your trailer wheel and hub area, and the removable center plug means if the Oil Level gets low, adding more oil to the system is a breeze. Simply remove the center plug and add oil through the opening. This is the Dexter Axle Part # 483990. If you are not sure whether this part will fit your trailer hub or not, you can check the part # number printed on the top of each cap. This is a standardized number, similar to bearing and race sizes, so if your current cap reads '483990' on the cover then this is the proper replacement. The Cap uses a threaded installation method that fits only the Tie Down Engineering Turbo Lube Threaded 3,500lb 5 Lug Hubs. These hubs are typically on a 3,500lb Dexter Axle. The Threaded installation combined with the included O Ring provides a leak proof seal.Specifications:- Black Plastic for a clean look- Oil Cap (Dexter part # 48399A)- Comes with Removable Rubber Plug and O Ring- Threaded Installation- Fits Tie Down Engineering 3,500lb Turbo Lube Hubs