Fasteners

Let’s start with the simplest fastener type: the nail. Although they come in several varieties, from roofing nails to ring shank nails, or straightforward carpentry nails, these fasteners are all characterized by the fact that they are straight, usually unthreaded, have flat heads, and are inserted by hammering.

Bolts are probably the most common type of fastener. They are used to hold unthreaded components together and work in tandem with nuts. They have external male threads on one end and a hexagonal head and are tightened using a wrench. Because nuts are used with unthreaded components and, unlike screws, don’t provide holding power by way of their thread, they need to be installed with the aid of a nut. Nuts are ringlike fasteners that are attached to the ends of bolts. The different types of bolts include hex-head bolts, eye bolts, carriage bolts and u-bolts.

Screws are similar to bolts. They also have a male thread that starts right at the tip and usually covers the entire length of the screw. The heads of screws can come in many shapes and sizes, and there is an astonishing array of screws for all kinds of projects and materials. Unlike bolts, screws rely on their threads to maintain their hold. Most screws are self-tapping, meaning that they cut a thread into the material as they are screwed in. Among the many different types of stainless steel screws available are wood screws, deck screws, hex lag screws, self-drilling screws, and machine screws.

Rivets are permanent fasteners that can be used to fasten all kinds of materials. They are incredibly lightweight and have a low profile against the surface of the material being fastened. Holes do not need to be threaded when rivets are used, but a special gun – a pop riveter – has to be used for application. Once a rivet is in place, it forms a permanent bond and cannot be removed. Rivets are preferred fasteners for the aerospace industry.

Washers are rings that are used in conjunction with nuts and bolts, being placed under the heads of nuts, joints or axle bearings. They are used for several different purposes, such as to alleviate friction, to allow more even distribution of pressure from the nut on the fastened component, to eliminate leakage, isolate components or prevent loosening due to vibration.

Tensile testing is used to measure the tensile strength of a fastener. Tensile strength is the maximum amount of tensile stress that a fastener can withstand before it breaks.

Yield testing is used to measure the yield strength of a fastener. Yield strength is the stress at which a fastener begins to deform plastically.

Fatigue testing is used to measure the fatigue strength of a fastener. Fatigue strength is the maximum amount of cyclic stress that a fastener can withstand before it fails.

Torque testing is used to measure the torque required to tighten a fastener to a specific preload. Preload is the amount of force that is applied to a fastener when it is tightened.

Corrosion testing is used to measure the resistance of a fastener to corrosion. Corrosion can cause fasteners to fail prematurely, so it is important to ensure that fasteners are resistant to corrosion in the environment in which they will be used.