Several variations of vest pocket pistols were manufactured. First was called Model 1920 by the Sauer firm. We usually refer to it as Model 1924. Pistol, as well as all other W.T.M. examples, were designed to carry in your pocket. Quite small in size and found only in 6.35mm or .25 ACP caliber. Later in 1928, an updated version became available and was referred to as Model 1928. These differed in internal parts design and slide configuration. Bottom of grip marked "Cal.6.35.28.". Last version appeared in 1933 and still utilized same grips, but trigger and other small parts differed. All three were available in blue or nickel finish, engraving and fancy grip material. Very few Model 1933 had stainless steel (NIROSTA marked) barrels.