The Third Generation
Beginning in 1996 the GLOCK pistol frames went through a few changes. Most significant are finger grooves and scalloped thumb rests on the grip. The GLOCK accessory rail was soon added after the introduction in 1996. Internal changes included beefier locking blocks and the rear slide tabs in the frame are smaller than in 2nd generation frames. The earlier production 3rd generation models are commonly referred to as 2.5 generation pistols. These so called 2.5 generation pistols are without the accessory rail, or the Loaded Chamber Indicator. The Loaded Chamber Indicator was added around 2006, due to ATF regulations. This addition also required a new design spring loaded bearing.
The 21SF was introduced in 2007. It was developed to compete in U.S. Military weapons trials, in an attempt to bring the .45ACP back as the U.S. Military side arm. 2009 saw the addition of 20,29&30SF models. The "SF" stands for "Short-Frame". They have a 2.5 mm (.10 inch) shorter trigger travel and the heel of the pistol is narrowed by 4 mm. The reason these modifications to the grip were done to more closely match the Beretta 92FS grip size. SF magazines have a cut out on the front of the body for the ambidextrous release as well as the regular release cutout. Some of the 21SFs had a 1913 style picatinny rail instead of the traditional GLOCK accessory rail.
Early 3rd generation 9MMs used the two pin frame, except for 26, until roughly 2006 when all remaining two pin frame 9MM models went to the 3 pin frame. GLOCK 29 & 30 received the accessory rail, and they are the only subcompacts to have accessory rails. There was also a 28 .380ACP added in 1997. I was a subcompact, three pin frame, but this one like the 25 is not for sale in the U.S. due to ATF regulations.
The last GLOCK pistol imported by GLOCK in Smyrna using the seven digit, US ending serial number was in November of 2002. The first imported six digit serial numbered GLOCK was serial number FDEOO1.
The first two baby GLOCKs, the 26 9MM and 27 .40S&W were introduced in 1996.
The GLOCK .45GAP was introduced with the 37 in 2003 with the 38 & 39 soon following. The .45GAP and accompanying pistols were developed for U.S. Law Enforce Agencies to bring .45ACP power to the smaller 17,19 and 26 pistol frame family. The round is loaded to .45ACP+P pressures.
The last of the 3rd generation GLOCKS, that could be considered a 3.5 generation pistol, were the RTF2s, the first of which, the model 22 was released in November of 2009. The RTF2s have a modified grip texture that uses lots of little raised dots set in a grid pattern. It is called the Ruff Texture Frame 2, being that it is the second version of GLOCKS ruff textured grips. The only other change made were the slide serrations being changed from the normal straight design to a curved gill serration. The gill serrations were produced on the slides of .40S&W (22 announced January of 2009 & 23 announced November of 2009) and 9mm (17 announced May of 2009 & 19 announced November of 2009), although, later productions of GLOCK 17, 19, 22 & 23 are produced with normal straight slide serrations. There is also a 21SF RTF2, which is the only model of RTF2 that has straight serrations for production run guns. Also, the 21SF RTF2 was a limited production run for law enforcement and those that are out there on the civilian market are over run quantity of the original limited production numbers.
The Fourth Generation
The most recent evolution for GLOCK pistols arose in the beginning of 2010. A newly designed grip texture, referred to as RTF or RTF3 is GLOCKS 3rd version of the Rough Textured Grip design. It differs from the RTF2 style in that the small dots are replaced with slightly larger squared dots in a tighter grid pattern. A new dual spring guide rod assembly replaced the old captured spring assembly. Later production 4th generation pistols have an updated spring set. The dust cover is larger to accommodate the new recoil spring assembly. There were also some various internal component changes. The magazine release is a reversible unit, which is now standard. Earlier generation magazines can be used in 4th generation pistols, but only when the release button is mounted on the left side of the grip, meaning released by right hand thumb when the right hand is the firing hand. 4th generation magazines can also be used in previous generation models. The most notable changeable to the grip are the addition of a changeable back strap package, which allows for 3 different customizable lengths between the front and back straps.
Models by frame pin variation. Two pin early 17, 17L, 18, early 19, 25 and early 34. Three pin 20, 21, 22, 23, 24, 26, 27, 28, 29, 30, 31, 32, 33, 35 and 36. Approximately 2006 and up 17, 19 and 34 received three pin frames.
Subcompact and Compact models have serrated triggers. The .45ACP models have octagonal rifled barrel compared to hexagonal rifling on other models.
From 1982 to 1991 G17s were assembled & test fired in Austria. (Later pistols were assembled and test fired at GLOCK Inc. in Smyrna, GA.) These early production pistols are marked with an eagle and "NPv". The markings are proof marks and inspectors marks as required on Austrian pistols. The NPv mark means "Nitro Powder proofed", which is given to the pistol when it was test fired with 130% power proving loads.
I did not add the compensated or OD frame models because they were too hard to track.