The Glock 37 Gen4, in .45 G.A.P., introduces revolutionary design changes to this quantum leap forward in big-bore technology-our answer to muzzle flip and high velocity recoil. The Modular Back Strap design lets you instantly customize its grip to adapt to an individual shooter's hand size. The surface of the frame employs the new scientifically designed, real-world-tested, Gen4 rough textured technology. Internally, the new Glock dual recoil spring assembly substantially increases the life of the system.