-HeliCoil Thread Repair Kits are used for creating stronger internal threads in all metals and other materials by repairing damaged or stripped internal threads and regaining the original thread size. HeliCoil Thread Repair Kit creates longer lasting durable threads, avoids thread over-sizing, increases the possibility of higher torque application in weaker metals, significantly reduces the bolt breaking problems . Kits are available in M2 to M39 & UNC/UNF series 4-40 to 1-1/2 inch