Photo Courtesy of fellow Glockophile DJ Niner - wherever you are.
The picture is hopefully self explanatory.
Gen 1 & 2’s do NOT have light / accessory rails. Gen 3’s - 4’s have light / accessory rails.
All 1st generation Glocks are G17’s.
If you say, “Hey wait a minute, I own a 1st Generation G19″ - I say prove it by posting clear pictures of the gun with serial number.
(There was a VERY SMALL run of 1st Gen G19’s made for a Government agency trial - these are considered the “Holy Grail” of Glock collecting - along with near mythical fully transferable G18’s :) )
There is also a style which is commonly referred to a 2.5 Gen Glock (not pictured). These were made about the time of transition from 2nd to 3rd generation. They can be clearly identified by the lack of a light / accessory rail, yet the frame grip has finger grooves. The 2.5 gen Glocks are not common..
If you ended up here and have a question about values, dates of manufacture, or other technical issues please post them in the Glock section of the forums, or other appropriate sections.
General production dates (These are guidelines only):
Introduction through 1988 - Generation 1
Late 1988 through 1997 - Generation 2
Late 1997 through Present - Generation 3
2010 through Present - Generation 4
There are NO accessory / light rails on Sub Compact Glocks.
1st Generation Glocks have become collectible in their own rights. And of those, the very early “Pencil Barrel” variants are the most sought after.
Glock did some experimenting with various Grip mold “textures”. In addition to the RTF, there are RTF2 and RTF3, plus probably others I am not familiar with. All these would be on at least 3rd Generation Glocks.
Glock also experimented with different serrations or styles of serrations on the slide, where one normally grips the slide to chamber a cartridge. These different serration styles are commonly referred to as “Gills” - you get one guess why (Answer - they look like fish gills). These non standard slide serrations are on some 3rd gen or later Glocks.
4th Generation Glocks have changeable back straps to allow a greater choice of grip thickness for those with smaller or larger hands.
Some generations were or are being produced at the same time. For example, when Glock introduced the 4th generation, they did not stop producing the 3rd generation. And as of December 2015 both 3rd and 4th Generation Glocks are being produced.