Atlas Bipods M-LOK Flush Cup Rail Black. It has 5 usable slots and a flush cup allowing the use of Flush Cup sling swivels (not provided). The BT80 can be used for the attaching of any of our 1913 Picatinny rail mounted Atlas Bipods Accu-Shot Monopods or Folding Foregrip. It requires standard M-LOK sized slots for mounting. Specifications for Atlas Bipods BT80 M-LOK Flush Cup Rail: Manufacturer: Atlas Bipods Color: Black Length: 3.15 in Weight: 1.135 oz Finish: Type III Hard Coat Anodized Fabric/Material: 6061-T6 Aluminum Country of Origin: USA Package Contents: Atlas Bipods Bipods BT80 M-LOK Flush Cup Rail Two 10-24 x 3/8 Fasteners Two M-LOK Nuts Atlas Bipods BT80: Bipods BT80 M-LOK Flush Cup Rail Black