Purlin Bolts & Nuts can be used to fasten components together by means of through holes and securing with a nut at the other end or they are screwed into a tapped hole with the matching thread Material / Coating: Galvanised is a dull greyish colour and can be a little rough in appearance and is mainly used outdoors because of its superior corrosion resistance and proven longevity. Also known as HDG it is one of the best coatings for protection against rust. Galvanised fasteners have been used across many industries in Australia for over 150 years roofing steel buildings trailers bridges fencing power poles marina’s are just a few examples. Both have marking systems that make it possible to determine grade and class. An example is a ½” UNC bolt with 5 lines on the head is grade 8 and 3 lines is grade 5 both are regarded as high tensile. Metric bolts are slightly different if it has 4.6 then it is mild steel and 8.8 is high tensile. The markings on a stainless fastener indicate the grade of material and strength e.g. material G304 grade will have one of the following markings: A2-70 G304 A2 304 and G316 grade stainless will have one of the following: A4-70 G316 A4 316 Thread Pitch (Metric): Pitch means the distance between the peaks of two threads along a screw bolt or fastener expressed in millimetres (mm). Used when referring to Metric parts. For example a thread pitch of 1.50mm means that the distance between one thread and the next is 1.50mm 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 and Nut Australia is not responsible for any loss claim or damages arising therefrom.