This is a Bravo Company , model BCM-MCMR-1913-N3-BLK.
Bravo Company's BCM 3 Inch Picatinny Rail Section" Nylon" M-Lok Compatible Modular rail section is made of lightweight impact resistant polymer. It is made to the Mil-Standard 1913 Picatinny Arsenal Specifications and it features a snag resistant design while retaining Mil-Standards.
Features:
M-LOK® Compatible
Nylon