Ballista Copper Penetrator Insert Pack of 12. Experiments have shown that compared to standard diameter (.296) micro-diameter shafts increase penetration by up to 25percent The penetrator insert at the wide part comes in a standard size allowing the use of any broadheads. This penetrator insert can be used with any tip giving you full freedom to customize your bolts. Specifications for Ballista Copper Penetrator Insert - Pack of 12: Manufacturer: Ballista Color: Stainless Steel Fabric/Material: Copper Inner Diameter: 4.2 mm Outer Diameter: 6 mm Weight: 125 grain Package Contents: Ballista Copper Penetrator Insert - Pack of 12 Ballista BAL-PI-01: Copper Penetrator Insert Pack of 12