Caution: Avoid direct eye exposure to the laser beam. Laser radiation is emitted from the aperture. Specification:Housing Material: BrassLaser Type: Red LaserLaser Wavelength: 635~655mmMax Output Power: <5mWPower Supply: 2Pcs LR41 Batteries (NOT Included)Product Dimension (L*D): 23x9mmBattery Installation: Positive side facing outwards. Look at your button cell battery, you will see "+" on the flat side commonly, which means positive. And the other slightly rounded side is the negative side. Features:- The laser bore sighter cartridge fits 9MM caliber.- Great for the range and ensuring your tactical equipment is still zeroed in after travel.- It projects a straight laser beam allowing precise optical adjustments to sight in your scopes or sights.- Battery Installation: Simply twist the end cap counterclockwise to open the battery housing, insert 2pcs LR41 batteries and all anode facing outwards. Be certain that the batteries are all facing in proper direction.- Turn On: Insert batteries then turn the end cap clockwise until it's slightly snug. At this point you should see the red laser dot.- Turn Off: No off switch, you need to open the end cap and take the batteries out.- About Storgae: If you plan to store the boresighter for a long period of time without use, remove the batteries to preserve power, place the sighter in a cool, dry place. Package Included:1 x Laser Bore Sighter1 x User ManualBatteries not included, please consider it before order.