TAC Limited The Original GIS Scope Mount for Gen 3 & 4 Glock 17 19 20 22 23 31 32 34 35 37 38 Fits all Glock models with a front Picatinny-type accessory rail. (Gen 3, 4, 5) Accepts all Sights Designed to Fit a Standard Picatinny Rail. Original Sights Remain Functional Lightweight, Durable, Polymer Construction Adds a Front Underside Accessory Rail. Underside Rail Allows to Attach Light Laser or other Accessory Installs quickly with no Gunsmithing Needed