WITH MY LISTINGS I TRY TO USE GUN FRAME SIZES SINCE THAT IS HOW HOLSTERS ARE MOSTLY FITTED.  Most grips too.

This is a general idea, but custom grips, sights, ribber and oversized barrels can affect form holster fittings, especially the snug, wet molded ones.

Several frame sizes are standard for the makers and many have been used for over 100 years.  Here are some types that I have discovered.


SMITH & WESSON REVOLVERS

I Frame An older and slightly smaller version of the J frame, usually on the pre numbered models S&Ws, some of the old Top Breaks.
J frame is used mostly for 5-shot .38 special and .32's, with some in .22 LR. Many versions, mostly 2" bbl pocket pistols. Some aluminum.
K frame is the most common S&W, the old-standby police issue of days gone by. Mostly 4" .38 and .357, some .32 and .32-20,etc. Rare in aluminum.
L frame is fairly new (1980s) and is a heavier size for .357 guns that are shot a lot with heavy loads, also a .44 special. No aluminum.
N frame is the big .44 mag, .44 special, .45 Colt,.45 ACP and the big frame .357. Heavy duty, but not at strong as the Ruger Redhawk. No aluminum.
X frame .460 S&W mag, .500 S&W mag.

COLT REVOLVERS

P frame Single Action Army (cowboy gun)
G, K, and Q various models of the .22 LR in SAA style
F frame Blackpowder guns (this is a strange one, they call all of the guns an F frame even though there are some rather noticeable size differences)
D Frame Detective Special
E Frame Officer's Model Match, Official Police and Trooper (original version)
I Frame Python
J Frame Official Police Mk III, Trooper Mk III and V, King Cobra, various variants of these

COLT AUTOS
.
O Frame 1911 pattern Colt Automatic
S Frame Colt Woodsman .22 Auto (and various match grade versions of same)