Recoil Control Thumb Rest for Glock Pistol Duty M Gen 1 to 3 (s/n before LXX) by Magloc #1750 1. Fits Gen 1, 2, 3 Glocks s/n before Lxx. Reduces muzzle jump by 70% (shooting weak hand only) 2. ,US Patent D472,599. does not fit Gen 4. Beaver tail length: Competition - 9mm (0.35") ; Duty - 2.7mm (0.11") 3. Wings can be modified with a file to fit different hand size. 4. Avoids slide cut on web of shooting hand, increase shooting speed and accuracy 5. Youtube installation instruction: https://www.youtube.com/watch?v=8SkSyF_hefY