This 2X40MR multi-reticle red dot sight is built with unique 2x magnification adapter. With the 2x adapter detached, it can be used as a 1x40 red dot sight. The sight is built with more visible and switchable two-color (GREEN/RED) reticle dot. It has integrated mounting rails that fit to Picatinny rails Specifications Overall Length: 4 1/4" w/o 2x adapter; 6" with 2x adapter attached 38mm center height Switchable 4 reticle dots illuminated in Green or Red Screw-on 2x Adaptor Lens Picatinny mounting system with a large knurled thumb screw Uses one CR2032 button cell battery(included). Also included with the sight are flip up lens covers for rear and front 2x adapter. CAUTION: Since zeroing involves actual shooting of live rounds, it should be done at an approved shutting range or equally safe area.