Top Grip Roofing Screws for fastening metal roof sheet to metal battens steel purlins or other steel substrates. This screw is perfect in steel roof construction where a heavy duty roofing screw is required. Top Grip: Top grip thread ensures a secure hold on sheeting prevents dimpling and stops the roof sheet moving down the shank when the roof is walked on. Material / Coating: Galvanised coated fasteners have been used for roofing cladding steel buildings trailers bridges fencing power poles outdoor furniture house framing fencing and marina’s for over 150 years. They are all variations of the original galvanise. All metal self drilling screws from Bolt and Nut Australia are guaranteed to comply to a minimum of Class 3 and extend to Class 4 and the ultimate of protection B8. To determine the TPI of a screw count the number of threads contained within an inch of length on the fastener. If the screw is less than an inch count ½” of an inch and multiply by 2 Length of Thread: Always choose a self driller with enough threads to fully engage in the base metal. For attachments to 1/4" base steel a self-drilling screw should have at least 1/4" of threads. It is helpful but not critical that the threads also engage in the material being fastened. The head of the fastener provides the bearing force for the material being fastened while the threads provide the clamping force in the base material Thread Length: Thread lengths have been included as a guide only. Due to stock being sourced from multiple suppliers variations do exist. The length of the drilling flutes determine the amount of drilling swaft that can be expelled and therefore the depth of metal can be drilled How to measure the length of a Metal Screw: Fastener length is generally measured from the point where the surface of the material will be when the fastener is installed to the end of the fastener. All material is advisory only and its use by anyone is entirely voluntary. Reliance on it for any purpose by anyone is at the sole risk of that person and Bolt a