Sig Sauer Tread Vertical Forward Grip Kit, M-LOK, Fits AR-15 Rifles, Black KIT-TRD-GRIP-FORWARD-BLK The Sig Sauer Tread M-LOK vertical forward grip kit is the factory replacement kit for the M400 Tread rifle series. It is compatible with any M-LOK mounting interface and includes a vertical grip" barricade stop" handstop" finger stop and short/long M-LOK panels.