Measuring cone style sure grip?

There's no real way to measure it because the ends are not wears down, it's the o.d. area that contacts the sure grip case and it's tapered so you can't measure it. You just visually inspect it and see if the cones are bottomed out in the sure grip case. I've seen them with very little to no wear and others that you can tell the cones were bottomed out for a long time cause their worn a lot. If it's original and still tight it's not worn bad. I have machined the side cones down in a few cone type sure grips which allows the cones to seat instead of bottoming out then according to what it looks like (how much wear is visual) I install shims accordingly. The thickest shims I ever had to install were .050" and it was worn pretty bad. By your description yours is in good shape so what I'd do is cut the ends down .030" so they won't bottom out for a long time and put some .020" shims in each side to regain preload.