These brackets are designed to fit the existing mounting holes in your chassis so that you can use these brackets to weld up your own harness bar for use with 4/5/6 point racing harnesses. The 2 large holes at the top of the main brackets fit the 1/2″ hole that the shoulder belt anchor normally attaches to and the smaller holes are for the holes in the aluminum rear window panel into the 1″ chassis tubes. Since the aluminum rear window panel is fitted by hand by the end builder, there is no guarantee that these holes will line up with your particular chassis, but they are slotted in order to accommodate most hole patterns. Designed to accept 1.5″ round tube. Welding required. I normally use a tube length of 56″.