These Forgefix high-low thread Concrete Frame Screws are Zinc Yellow Passivated for increased resistance to corrosion. They offer a stress free fixing, allowing close to edge applications. They are through-fixing, eliminating any need for marking and re-positioning when fixing batons etc. The Torx compatible head of the screw provides increased torque control. Supplied complete with a Torxcompatible bit. This product is extremely popular fixing for window and door frames. They are also now used as a versatile fixing for many applications in DIY, Joinery, Plumbing and Electrical trades. The Zinc Yellow Passivation process of electroplating is similar to the Galvanised and Zinc Plated processes but with the addition of a yellow dye. It offers an aesthetically pleasing finish, whilst still providing brilliant corrosion-resistance. By design, TORX compatible head screws resist cam-out much better than Phillips or Slotted screws. Where Phillips heads were designed to cause the driver to cam out, to prevent over-tightening, TORX compatible heads were designed to prevent it and to achieve a desired torque consistently. TORX compatible head sizes are described using the capital letter T, followed by a number. A smaller number corresponds to a smaller point-to-point dimension of the screw head. Only the proper driver can drive a specific head size without risk of ruining the driver or screw. High-Low Thread screws have an outstanding holding power in wood due to their alternating high and low thread heights.