The Kinetic Research Group Arca Heavy Spacer is designed to fit between your ARCA Rail and forend to increase the weight of your rifle in order to mitigate recoil and allow easier impact spotting and a quicker followup shot. NotesFits: KRG Whiskey-3, X-ray, and Bravo chassis.Use as many fasteners as possible to mount the rail to maintain rigidity.Does not work on 180-Series chassis.Using the ARCA Spacer Heavy alone on the forend is not recommended and will require shorter fasteners.