I have a smith & wesson model 624 with a four inch barrel in .44 special... this seems to be a decent gun... but I'd like to buy a holster... I want to buy a used leather holster, something like I could find on e-bay... cheap! Well, most S&W holsters have a number stamped on the back of the holster, like 21 39.... I can find nothing on the net to tell me what these numbers refer to... or how to determine which frame or pistol they fit! Can anyone out there help? I'd like a chart on pistol holster sizes for smith & wesson holsters!