The Contact Screw is what carries the electricity from the binding post to the front spring. While the machine is running, the front spring is constantly bouncing off the Contact Screw, so it is important to have a strong screw. Brass is a stronger conductor, so it is perfect for this tattoo machine part. The Brass Contact Screw is 32mm long, has a diameter of 3mm and is M3 metric. The thread length, or distance of the thread, is 0.5mm.