Size is correct. J is the smallest, primarily found in the .38 special 5-shot revolvers like the Chief's Special (Model 36). N is the largest, primarily used for the .44 Magnum, .45 Colt, .41 Magnum. The N frame was also used for the original .357 Magnum. S&W later chambered the .357 in the medium K frame (probably most notably known for the .38 Special Model 10 M&P) due to demand for a smaller/lighter revolver in .357 Mag. In 1980 S&W came out with the slightly larger/heavier (than the K frame) L frame to better handle the recoil and punishment that K frame .357's like the model 66 were experiencing. K & L frame models share the same grip size, but cannot use the same holster because of the L frame's otherwise larger dimensions.