Choose What’s Best For You. The XM is a waterproof switch assembly for SureFire's Millennium Universal and Classic Universal WeaponLights. It includes a system disable feature, click-on/off pushbutton switch and a plug-in momentary-on remote tape switch. The pushbutton and pressure-activated tape switches operate independently, providing switch redundancy. When choosing an XM switch model, the two digits after the "XM" indicate the cable length in inches. For example, the XM07 has a 7-inch cable. The seven-inch cable length works with most rifle/carbine applications.