Competition 2 M1 Recoil Control Thumb Rest for Glock Gen 1 to 3 S/n Before Lxx Competition 2 M1 forn Glock s/n fefore Lxx. US Patent D472,599. Reduces muzzle jump by 70% (shooting weak hand only) Fits Gen 1 to 3 Glock.. Beaver tail length: Competition M - 9mm (0.35") ; Duty M - 2.7mm (0.11") Wings can be modified with a file to fit different hand size. Avoids slide cut on web of shooting hand, increase shooting speed and accuracy Youtube installation instruction: https://www.youtube.com/watch?v=8SkSyF_hefY