This bronze bush is used in all primary gears and has a integral thrust surface for controlling end float on the primary gear. Thus not only is the ID critical but the thrust face must also be in spec in order to achieve the proper critical control of end float. Replacing the bushing in a gear is much more cost effective than replacing the entire gear. The gear itself rarely wears out- only the bushes! The gear for the pre A+ 1275cc engines are no longer available and thus bush replacement is the only answer.