These housing ends are CNC machined from alloy billet steel. They are for race use and have threaded holes for easy installation of caliper mounting bracket or backing plate. Designed for o-ring style sealed axle bearing. They are 1" wide with a 3.150" diameter axle bearing bore. The bolt pattern is 3.500" center-to-center across the top, 2.875" center-to-center across the bottom, and 2.375" center-to-center vertically. The bolt holes are 3/8"diameter. Kit contains a pair of housing ends.