These are commonly used in steel roofing. Aluminium versions are sometimes used for Aluminium cladding (to prevent Galvanic Corrosion from dissimilar metals). Lag Screw provide the greatest corrosion resistance, particularly when the superior Hardtec grade is used.

They are hardened by heat treatment and so have excellent drilling performance into metals like grade 410 BUT unlike grade 410, these grades have Molybdenum added to them and have corrosion resistant properties in line with the 300 series Stainless grades. Salt Spray tests show corrosion resistance equal or better to that of 304 grade and not far behind 316 Stainless Steel. They are an excellent screw!

Common types of nuts and bolts include barrels, cap nuts, cage, coupling, crushed, cross dowel, inserts, internal wrenching, knurled nuts, lugs, panels, plates, flange, Hex Nuts, plate nuts, split nuts, weld nuts, staked, swage nuts, self-aligning nuts, Carriage Bolts. They can be used for various applications. Mostly made from low or medium carbon steel, with minimum tensile yield strength of 420 MPa or 61 ksi, nuts and bolts are ranked mostly in classes between 5 to 10.

Hex nuts, usually known as finished full are used for fastening to a bolt when mechanically joining materials together. Hex nuts are mostly made from materials like brass, zinc plates, steel grade 8, stainless steel, silicon bronze, hot dipped galvanized and grade 2 chrome. Hot dipped galvanized and grade 2 chrome are most popular hex nuts because of being corrosion resistant. They are thick and are used mostly for exteriors and coastal areas. Whereas, the grade 2 chrome has a bright mirror like finish providing sharp looks for a variety of applications.

However, even though nuts and bolts stay together through a combination of interlocking threads and torque it is possible for grip of the pair to loosen over time even though the nut was originally properly tightened. Fortunately, it is possible to remedy this by using smooth metal discs called 'washers'. Washers provide a smooth surface for the nut or bolt head to grip and can help to distribute pressure evenly.

A bolt is basically a screw with a blunt end instead of a sharp one. Both of these types of fastener have a 'thread' which is essentially a raised ridge winding in a spiral around the shank of the bolt or square headed screws . The main difference between them, however, is the fact that a bolt is invariably accompanied by a nut to function effectively. The nut typically also has a thread which allows it to be twisted onto the bolt so that the two adjacent surfaces that require joining are squeezed between the nut and the bolt head and thus held together.