The IronRidge BHW-SQ-03-A1 T-Bolt Bonding Hardware comes with a square bolt and is for attaching and bonding the IronRidge FlashFoot2, FlashVue, Halo UltraGrip and Slotted L-Feet to the XR Rail. An added feature is that it can be installed with the same socket as the rest of the system saving you valuable time.