what is the standard size trailer hitch ball

If you have a hitch mounted bike rack, then you might want to check the top of the trailer couplet for the size of the ball diameter required. The size is usually stamped there. Recreational and light commercial hitch balls come in a variety of sizes including 1 7/8", 2", 2 5/16" and occasionally 3". In general lighter trailers use smaller hitch balls.