The GLOCK 17 Gen4 in MOS Configuration is a full-sized, optics-ready pistol perfect for duty and self-defence. The MOS Configuration makes it easy to mount a miniature reflex sight on the pistols slide without the need for a new slide or separate mounting system. Other features include the modular backstrap design; the dual-recoil spring assembly substantially increases the life of the system and the enlarged reversible magazine catch easily accommodates left or right handed operators. MOS pistols come with a cover plate and four different plate options that fit the sights from the most trusted optic manufacturers in the industry.