Phillips, Flat, Hi-Lows. High-Low thread for use in plastic, nylon, wood or other low-density materials. Thread design reduces driving torques, enhances resistance to thread stripping, improves pullout strength and lessens the risk of cracking the work piece. Flat head screws are used when protrusion of the fastener above the mating surface is unacceptable. Typically 100 degree flat or for fastening softer materials, 82 degrees flat.