I've noticed that on the mid sized models (19, 23, ect.) the width of the top and bottom grooves are narrower than the center groove. If you look, the top and bottom grooves have two rows of "checkering" while the center one has three. The full sized and the sub-compact models, each have three rows of checkering on all of the grooves, and the grooves are of the same width. My hands (large) fit the full-sized very well. I also fit the sub-compact perfectly (though my little finger wraps under the butt, much like on a single-action revolver). I do not find the mid-sized grips usable. The ridges rest on my fingers, not between them. Just my observations.