This is a replacement Integral-Style Trailer Disc Brake Rotor, Meaning that the Trailer Hub and Brake Rotor are made as one single piece. The Integral Rotor features six 1/2" diameter studs, in the standard 5 on 4.5" bolt spacing pattern, and comes with the Grease Seal and read bearing Pre-installed. The Front Bearing, Spindle Hardware, and Dust Cap are also included with this Replacement Trailer Disc Brake Rotor kit. The Bearing Sizes that are included with this Rotor are Inner Bearing 68149 (1 3/8" inner diameter) and Outer Bearing Number 44648 (1 1/16" inner diameter). The Grease Seal Measures 1.719 inches inner diameter. This Bearing and Seal Size Combination is common on a lot of trailers, but it is not the only bearing and seal size combination for 5 Lug Trailers, so be sure to double check your trailer's bearing and seal sizes first to make sure this will work as a suitable replacement prior to purchasing.