linux; Ours were mounted offset to one side or the other, depending on if they were lefties or right handed shooters and they wanted to use a finger or thumb to activate their light. It's really a simple operation. Once you find the spot you want the mount/light to be, tape the mount, mark the screw holes, drill through the handguard and attach mount. Be sure to use Loctite on the nuts to keep them tight. Hope this helps.