Bolts & Nuts – Fasteners
Bolts are threaded fasteners with an external male thread that attaches to a female threaded nut to fasten material together. As a threaded fastener they are similar to a screw.
While there is overlap between what is a bolt and what is a screw there are some defining distinctions in there intended purpose.
Bolts, with the aid of a nut, are designed to assemble, fasten, or hold two components that aren’t threaded or will not accept being easily threaded. A bolt and nut apply an axial clamping force working as a perpendicular shear force against the components that are being held together.
However, screws are used with components that contains its own internal thread or may be formed by the installation of the screw itself. This means there is an overlap between these fasteners. Where a fastener forms its own thread, or “carves” a threaded groove, in the component being fastened, it is called a screw. Because this groove is carved or cut into the component substrate a screw is typically tapered. This also means that a screw does not require the use of a nut.
Bolt Grades
Grade of Bolts – Hardness
A bolt can come in many grades, or level or hardness. The higher the grade the higher the steel and the more pressure it can withstand. These grades can be identified based on the marking on the head of the bolt. Not shown here are Grade 5.2 and 8.2. These are similar in strength, but vary in composition and length. For example an 8.2 bolt will have similar strength but is limited to 1 inch diameter and is composed of Low carbon martensite steel instead of the medium carbon. From what we can tell many of these grades are less used the the SAE 2,3,5,6, and 8. SAE are “Standard” or “American English” hardware in contrast to “Metric.” SAE bolts can come in coarse or fine thread.
Fine Thread Bolts / Coarse Bolts
Bolt Lengths & Bolt Threads
A coarse bolt is great for quick and general fastening. The advantages to a fine thread, generally speaking, is that
(1) A fine thread is stronger than a coarse thread in regard to both in tension across the larger stress area and shear due to their diameter. And (2) fine threads are less likely to loosen since the thread incline is smaller. This means that the “off torque” is also smaller.
Washers
Washers for bolts
In order to expand the holding diameter, which helps prevent pull-through and improve fastening, a washer is ideal. Additionally a washer can improve the “lock” between the bolt, nut, and substrate or component.
Types of Washers
Below are types of washers and their uses:
Flat – These general use flat washers are positioned under the head of a bolt or nut in order to provide a smooth bearing surface and distribute the fastener load over a wider area.
Fender – Same use as flat but narrow diameter and larger coverage area
Finishing – Finishing washers protect the underlying material while improving the appearance of the countersunk screw.
Split Look – Lock washers are specially designed to keep threaded fasteners from loosening. They prevent vibrations and some have external teeth to prevent rotation. These washers are often found in airplanes and in structural applications.
External Tooth Lock – In external tooth lock washer has teeth that extend radially outward to bite into the bearing surface. Like internal tooth lock washers, they are designed to prevent a nut or bolt head from loosening with the strut action of the teeth. They work best with larger screw or bolt heads. External tooth lock washers provide maximum torsional resistance.
Internal Tooth Lock – An internal tooth lock washer has teeth that extend radially inward to bite into the bearing surface. The internal tooth lock washer is designed to prevent a nut or bolt head from loosening with the strut action set up by the teeth. The teeth, also, absorb shock and vibration. The teeth abrade the grounding surface in electrical grounding applications to improve the electrical connection.
Square – Square nuts have a large surface area, which resists tightening and loosening. Square nuts are commonly used in furniture, metal channels, and railroad applications.
Dock – Dock Washers are used in construction applications where low carbon, thicker washers are specified.
Ogee – Fastenal Ogee washers are oversized with a large bearing surface designed specifically to prevent heads from being pulled through wood like materials. Fastenal Ogee washers are durable offering a long lasting finish for an application.
Nuts For Bolts
Bolt Nuts
Nuts are a big part of the fastening system utilizing bolts, and there are many types. Some build in a locking mechanism and others allow for fast hand fastening such as a wing nut.
Types of Nuts
Here is a list of nuts and description:
Hex – Hex nuts are six sided general purpose fasteners with internal screw threads.
Heavy Hex – Heavy hex nuts are somewhat larger than a standard hex nut, compatible with high strength and large diameter bolts.
Nylon Insert Lock – Nylon Insert Lock is a kind of locknut. It is a nut with a nylon collar insert that resists turning.
Jam – Jam nuts are used as a second nut threaded over a bolt to prevent the first from loosening, or in applications where there is not sufficient space for a standard nut.
Nylon Insert Jam Lock – Same thing for Nylon Inser Lock.
Wing – A wingnut or wing nut is a type of nut with two large metal “wings”, one on each side, so it can be easily tightened and loosened by hand without tools.
Cap – Cap Nuts are used to cover exposed threaded stud, rod and bolt ends with a dome-like cap. This provides safety and a finished look to the exposed threaded end.
Acorn – Acorn nuts, also known as cap nuts, feature a domed fastener head which protects screws and bolts from stripping, allowing for reuse after maintenance.
Flange – Flange nuts have a washer-like base to distribute pressure over a greater surface area and ensure the fastener stay tight. They are commonly used in manufacturing assembly lines where operations are speeded by using a single fastener instead of a nut and washer.
Tee – Often used in furniture to provide an internally threaded surface for fasteners, tee nuts are inserted into materials like wood, composites, and particle board. They feature a head style that digs into the surface to ensure retention and leave the nut flush with the surface.
Square – Square nuts have a large surface area, which resists tightening and loosening. Square nuts are commonly used in furniture, metal channels, and railroad applications.
Prevailing Torgue Lock – Prevailing Torgue Lock is a built-in locking feature develops full locking action as soon as these nuts are engaged with the bolt threads. They must then be wrenched to final seated position.
Types of Bolts
Types of Bolts
There are many types of bolts. While some bolts are indeed used for generic purposes some have very specific designs to aid in specific requirements. For example while a carriage bolt is ideal when fastening wood and metal it also allows for some security given the method of tightening on the bolt end is build beneath the head in a square insert held by a square opening in the metal substrate, unlike other bolts that may have a six sided top that can be unbolted. As long as the nut side of the duo is not accessible it will provide a little security.
Types
Here are some types of bolts and what they are used for:
Carriage Bolt – A carriage bolt, coach bolt or round head square neck bolt is a form of bolt used to fasten metal to wood.
Eye Bolt – Eye bolt is a bolt or bar with an eye at the end for attaching a hook or ring to.
Lag Bolt – Also commonly known as lag bolts, lag screws are some of the toughest fasteners. These extremely sturdy fasteners are usually used to connect heavy lumber or other heavy materials that are bearing an intense load. These screws differ from normal wood, self-drilling or sheet metal screws.
Flange Bolt – Flange bolts are identifiable by a ridge below the bolt head. This built-in washer distributes the clamping load over a greater area. Commonly used by assembly line workers in the automotive industry, these bolts are designed to provide the same holding power as a washer.
U -Bolt – U-bolts are versatile fasteners used to secure pipes, conduit, cables, and machinery, or as an anchor in foundations and roofs.
J – Bolt – J bolts are a very common and durable fastener that many contractors use when erecting a new building. Homeowners can also use the threaded fasteners when building a garage, building a new foundation, or simply attaching a new wall to concrete.
Shoulder Bolt – Shoulder bolts, or shoulder screws, have a long, unthreaded, cylindrical shoulder that allows for the rotation of attached parts like pulleys, gears, moving parts of engines and mechanical assemblies, and rolling wheels. These screws are also used to attach stripper plates. The socket head enables high torque fastening with limited clearance.
Elevator Bolt – Elevator bolts are often used with canvas or other soft, pliable materials. The large diameter, flat countersunk head keeps them from pulling through the material. Also known as belt bolts, elevator bolts are also known for a shallow, conical bearing surface, an integrally-formed square neck under the head and a unified thread pitch.
Sex Bolt – A sex bolt, (also known as a barrel nut, barrel bolt, ‘Chicago screw’ or post and screw), is a type of fastener (nut) which has a barrel-shaped flange and protruding boss that is internally threaded.
Machine Bolt – Machine bolts are used to fasten wood to wood, wood to metal and metal to metal.
Stove Bolt – A stove bolt with a slotted head, used in the assembly of wood-burning stoves constructed from sheet metal.
Hanger Bolt – Hanger bolts have threaded areas at both ends: a lag screw thread at one end and machine screw thread on the other. They are designed for insertion into a pre-drilled hole and are ideal for overhead applications, such as suspending electrical wiring or sheet metal from wooden structures.
Timber Bolt – Timber bolts are also referred to as dome head, fender head, safety head, and mushroom head bolts. In the Pacific Northwest, they are referred to as an economy bolt. They are used in marine and wood applications.
Draw Bolt – Draw bolts used to draw counter-tops together.
Bolt heads
Like screws, bolts use a wide variety of head designs. These heads engage with the tool, such as a wrench, used to tighten them. As described above some bolt heads, such as the carriage bolt, lock the bolt in place, so that it does not move and a tool is only needed for the nut end.
While screws use tools that fit internal and bolts primarily utilize exterior fitting tools such as wrenches or sockets there are some overlaps. This is primarily in using Allen or Torx heads; hexagonal or splined sockets. These designs are more modern and can carry a considerable torque.
Full Bolts Infographic:
