This is a Round Spindle Washer for 3/4" inch Trailer Axle Spindles. This is a standard round Trailer Spindle Washer, this style is typically used on Trailer Spindles that do not have a grease fitting, and that use Cotter Pins to secure the Hub and bearings into place. This washer would install after your outer bearing is installed, but before the Castle Nut and Cotter Pin or Cotter Key. The inside diameter of this Washer is 1 3/4".