This is a Surefire Weaponlight known as the M600 Scout, model M600V-B-Z68-BK.
The SureFire M600V provides both white light and infrared illumination powered by a single 123A battery. Select the appropriate spectrum for the situation at hand by simply rotating the bezel. This rugged Weapon Light features SureFire's proprietary TIR lens" a far-reaching" high-intensity beam with ample surround light. The rugged M600V easily and securely attaches to MIL-STD-1913 Picatinny rails via its integral thumbscrew clamp and is activated by clicking its pushbutton tail cap switch. Constructed of lightweight aerospace aluminum" with a Mil-Spec Hard Anodized finish" and O-ring sealed to keep out the elements" the tough M600V will endure combat-like conditions without any sacrifice in weapon maneuverability. Fits: Rifles" carbines" or submachine guns with a MIL-STD-1913 or STANAG 4694 ("Picatinny") rail on the forend.
Features:
Virtually indestructible IR/white LEDs
TIR lens shapes
Thumbscrew mount attaches quickly & securely to MILSTD-1913 rails