GLOCK 19 Gen5 MOS GLOCK enhances the desirability of the already near-perfect Gen5 model with the addition of the Modular Optic System (MOS). The slide is precision machined to provide a mounting system for popular optic sights. With multiple adapter plates, you can quickly and easily mount miniature electronic sights to the rear of the Gen5 GLOCK slide, which has front serrations for easier and quicker manipulations.