This is the ball center for use in all RockJock 2 1/2" diameter Johnny Joint® rod ends. Ball is CNC machined steel, heat treated, features a .5625" thru bolt hole and a 3.350" overall mounting width. For use as a rebuild part or for those building up their own arms and joints. We use this center in our Ford Mustang Currectrac® upper control arms. Sold each.