H... Glossary of Fastener and Fixing Terminology

Half dog point, hammer-drive-screw-hard-joint-hardness-of-steel-hardened-washers-head-marking-heat-tightening-helical-spring-washer-heli-coil-hexavalent-chrome-high-strength-friction-grip-bolts-hold-drive-bolts-holo-krome-hook-bolt-hook-nuts-hot-bolting-hot-dip-spun-galvanised-hot-forging-hydraulic-tensioner-hydrogen-embrittlement






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The most popular of the Dog points, half as long as a full dog point; used on short screws for the same purposes as the full dog point, but in a shallower hole or slot.  Half Dog  Full Dog 


A piloted, multiple threaded screw with a large helix angle, used for permanent applications. It forms a mating thread as it is hammered or pressed into a prepared hole.  Product


A joint in which the plates and material between the nut and bolt bearing surfaces have a high stiffness when subjected to compression by the bolt load. A joint is usually defined as hard if the bolt is tightened to its full torque and it rotates through an angle of 30 degrees or less after it has been tightened to its snug condition.


The force under the head of a bolt or nut can exceed the compressive yield strength of the clamped material at high preloads. If this occurs excessive embedding and deformation can result in bolt preload loss. To overcome this hardened washers under the bolt head can be used to distribute the force over a wider area into the clamped material. A more modern alternative is to use a flange headed nuts and bolts.  Product


Hardness grades of steel click for table


Used to identify the material and manufacturer in a fastener such as a bolt or cap screw. The marking is either raised or indented to specifications.  


Heat tightening utilises the thermal expansion characteristics of the bolt. The bolt is heated and expands: the nut is indexed (using the angle of turn method) and the system allowed to cool. As the bolt attempts to contract it is constrained longitudinally by the clamped material and a preload results. Methods of heating include direct flame, sheathed heating coil and carbon resistance elements. The process is slow, especially if the strain in the bolt is to be measured, since the system must return to ambient temperature for each measurement. This is not a widely used method and is generally used only on very large bolts.


A split type of spring washer whose purpose is to prevent self loosening of the nut or the bolt. The idea or principle behind the helical spring washer is for one end of the tang of the washer to indent into the fastener (the nut or bolt head) and the other into the joint surface so that any loosening rotation is prevented. Junker in his paper in 1969 on the cause of self-loosening of fasteners concluded that this type of lock washer has limited ability to lock. This type of washer is sometimes called a spring washer. spring lock washer or sometimes a split lock washer. Product


Coil of wire used as an insert to accept a screw or bolt and adding holding power by forcing itself between the fastener and the walls of the recess when the fastener is driven in.  

Wire threaded insert is typically used for tapped hole repair or to improve the thread stripping strength of softer metals such as zinc and aluminium. The inserts are assembled into a previously tapped hole using a special driving tool. Thread locking compounds are frequently used to secure the insert if the assembly is subject to vibration.  Product


Trivalent chromium passivation Cr3 has replaced the toxic Hexavalent chromium on fastener coatings.   


Sometimes abbreviated to HSFG bolts. Bolts which are of high tensile strength used in conjunction with high strength nuts, load indicating washers and hardened steel washers in structural steelwork. The bolts are tightened to a specified minimum shank tension so that transverse loads are transferred across the joint by friction between the plates rather than by shear across the bolt shank.  Product

HOLD AND DRIVE BOLTS              

Special bolts that have a tang at the threaded end of the shank. This tang is gripped by the tightening tool during assembly so that the reaction torque is absorbed whilst the nut is tightened from the same side. Such bolts allow what used to have to be done by two men to become a one-man task.


Since its formation in the USA in 1929, Holo-krome has been at the forefront of fastener development and innovation. The company was organized around what was a revolutionary idea at the time the manufacture of socket screws by metal forming or heading rather than machining; later invented a "Cold-Forged" process in which the metal is pre-warmed to improve its plasticity for forming.  Product


A "bent bolt" having the unthreaded end bent to form a hook, such as a round bend, square bend, right-angle bend, or acute-angle bend hook bolt.  Product


Hook nuts are also known as bearing nuts and are used to lock bearing onto shafts and shafts onto housings.  Product


This term is used for the completion of maintenance work on a bolted joint when the joint is under loading. This can involve the replacement of individual bolts. There are risks both to the joint itself and to health and safety associated with this technique.


Applying a coating of molten zinc to a fastener by dipping and then spinning off the excess; under cutting or retapping of nut threads is often required  Finish


Forging is the process of forming a product by hammering or the displacement of material under force. When worked above the re-crystallisation temperature having been pre-heated, it said to have been hot forged. more detail   Hot


A hydraulic tool used to tighten a fastener by stretching it rather than applying a large torque to the nut. After the fastener has been stretched, the nut is run down the thread to snug up with the joint, the hydraulically applied load is then removed resulting in tension being induced into the fastener.


Steel fasteners exposed to hydrogen can fail prematurely at a stress level well below the materials yield strength. Hydrogen embrittlement occurs in fasteners usually as a result of the part being exposed to hydrogen at some time during its manufacturing process or coating process and it can also occur through in-service corrosion.

Electroplating is generally considered to be a major cause of hydrogen embrittlement in steel fasteners due to the absorption of hydrogen during this process. Higher strength steels particularly 12.9 grade are more susceptible to hydrogen embrittlement than lower strength steels, however it is considered that there is no lower strength limit. As a rule of thumb, steels below 10.9 grade are considered to be far less susceptible. more detail





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