This is a Bravo Company Mount known as the KeyMod, model BCM-SLM-KM.
Bravo Company's BCMGUNFIGHTER Modular Scout Light Mount KeyMod Version is designed for use with Surefire's Scout Light mounting interfaces. There are multiple mounting holes for ideal rail placement and designed to mount on the 3 or 9 o'clock rail positions. Its durable aluminum construction is intently designed to be low-profile and snag free. Being fully ambidextrous it is made to mount flush or cantilever off either the left or right side of the rail system.
Features:
Compatible with- M300 MINI M600AA M600 ULTRA M600P FURY M300V MINI and M600V
NOT compatible with- M620V M620P FURY or M620 ULTRA