The .580 or 58 and the .600 or 60 are the core diameters of the grips. Putting a .580 grip on a shaft butt diameter of .580 gives you a "standard" grip size. The same for the .600 - putting a .600 core grip on a .600 butt diameter shaft, gives you a standard size grip. If you put the .580 grip on a .600 butt diameter shaft, you get a grip size of 1/64" oversize. Below is a link to a grip sizing chart that will explain more.
Date published: 2017-02-16