Spax Silver Pozi Screw 3.5mm X 20mm Box of 200 - Spax silver screws are a universal screw with a flush countersunk head that can be used in multiple applications and with a range of materials including timber, ply and mdf to name a few. With the 4CUT point No pre drilling is required on many material, though some materials may require pre drilling. Spax silver screws come in a variety of lengths and thicknesses and use a PZ2 bit.