D... Glossary of Fastener and Fixing Terminology



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A high performance zinc flake surface coating that can be applied to fasteners. The coating consists of passivated zinc flakes that are stoved onto the metal surface. The coating can be coloured and eliminates the risk of hydrogen embrittlement associated with electroplated metal. Zinc flake


The point at which there is zero pressure at the joint interface as a result of forces applied to the joint. If the applied force is increased beyond the decompression point, a gap will form at the interface. Analytically, a criteria of joint failure is often taken as when the applied force on the joint reaches the decompression point. This is because forces acting on the bolt(s) can dramatically increase at this point. Loading beyond this point can also result in fretting at the interface that will lead to bolt tension loss that will subsequently lower the decompression point. This process can continue until bolt failure does occur. The failure can be by fatigue or other mechanism but the underlying cause was loading of the joint beyond the decompression point. It is for this reason that it is frequently taken as a failure criteria in analysis work.


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


The design form of an internal or external thread is the thread form in it's maximum metal condition. It is the same as the basic thread profile except that the thread roots are rounded. If either the internal or external thread form exceeds the design form of the thread profile then a potential interference exists.


German standards, Deutsches Institut fur Normung. Fastener products are produced to these standards with the standard number after the DIN for example: DIN 912 socket cap screw metric, DIN 933 hexagon screws.  DIN Standards


Direct Tension Indicators (DTI's) is a term used to describe load indicating washers. Projections on the face of the washer (usually on the face abutting the bolt head or nut) that deform under loading as the bolt is tensioned. An indication of the tension in the bolt can be made by measuring the gap between the washer face and the nut or bolt head. The smaller the gap - the greater the tension in the bolt. Commonly used in civil rather than mechanical engineering applications.  Product


Coned-disc spring, conical spring, disc spring, or cupped spring washer, are types of spring shaped like a washer. It has a frusto-conical shape which gives the washer a spring characteristic.   Product


A cylindrical extension, or pilot, of diameter smaller than the minor diameter of the thread, commonly equal to about D/2 in length, with a conical section between it and the thread; usually used as a pilot in assembling or as the end of a set screw projecting into a fairly deep hole or slot.  Product


Also called an acorn nut, usually hexagon with a sealed end  it has a hexagon base and a domed top that it prevents contact with the threads, Products.


Threaded at both ends with coarse fit threads to take nut assembly.  Product


Used as a holding pin with chamfered on one end. Extensive range in inch and Metric including pull (extractable) Dowels   Product


One end has a Gimlet point, threaded similar to a Lag Bolt. The other end is parallel threaded. Used in joining two wooden members such as a leg to a table top. Product  


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


Resistance to relative movement of two bodies that are already in motion.



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dacromet coating and decompressions point along with de-embrittle detail. design-form-of-thread-din-direct-tension-indicators-dog-point-double-end-stud-dome-nut-dowel-pin-dowel-screw-drive-screw-dynamic-friction-effective-diameter-effective-nut-diameter