These Forgefix high-low thread Concrete Frame Screws are Zinc Yellow Passivated for increased resistance to corrosion. They offer a virtually stress free fixing, allowing close to edge applications. They are through-fixing, eliminating the need for marking and re-positioning when fixing batons etc. The Torx compatible head of the screw enables increased torque control. APPLICATION: Extremely popular fixing for window and door frames. 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 having excellent resistance to corrosion. 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 excellent holding power in wood due to their alternating high and low thread heights.