ERGO M-LOK® MODULAR FREE FLOAT RAIL SYSTEM. $ 125.00 – $ 155.00. Comes standard with a 3-pack of M-LOK™ or KeyMod™ Rail covers in black and an 18 slot ladder in black for the Picatinny Rail. 6061 T6 Construction, Type III Black Hard-Coat Anodized. CNC machined lightweight one piece free float design.