<P> A mid-life upgrade to the Glock pistols involved the addition of checkering on the front strap and serrations to the back strap . These versions, introduced in 1988, were informally referred to as "second - generation" models . To meet American ATF regulations, a steel plate with a stamped serial number was embedded into the receiver in front of the trigger guard . </P> <P> In 1991, an integrated recoil spring assembly replaced the original two - piece recoil spring and tube design . The magazine was slightly modified, changing the floorplate and fitting the follower spring with a resistance insert at its base . </P> <P> In 1998, the frame was further modified with an accessory rail (called the "Universal Glock rail") to allow the mounting of laser sights, tactical lights, and other accessories . Thumb rests on both sides of the frame and finger grooves on the front strap were added . Glock pistols with these upgrades are informally referred to as (early) "third - generation" models . Later third - generation models additionally featured a modified extractor that serves as a loaded chamber indicator, and the locking block was enlarged, along with the addition of an extra cross pin to aid the distribution of bolt thrust forces exerted by the locking block . This cross pin is known as the locking block pin and is located above the trigger pin . </P> <P> The polymer frames of third - generation models can be black, flat dark earth, or olive drab . Besides that, non-firing dummy pistols ("P" models) and non-firing dummy pistols with resetting triggers ("R" models) have a bright red frame and Simunition - adapted practice pistols ("T" models)--a bright blue frame for easy identification . </P>

When did the glock gen 3 come out