P... Glossary of Fastener and Fixing Terminology

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Palnut is a locking device for nuts made of stamped sheet metal. The palnut is screwed on the bolt on top of an ordinary nut and has a series of protruding barbs that lock the nut in place when the nut is tightened. The Palnut itself is reusable. A Palnut should not be used as a substitute for a positive locking device such as a prevailing torque nut, castellated or a slotted nut   Product


The pan head has a flat under head bearing surface and a shallow oval-shaped head profile similar to a frying pan.  Product


The Parabolt is a through (Thru) bolt for construction fixing into concrete.  Product


A screw designed for use with particle board also called chipboard. Plywood has the potential to feather off in sheaves when extreme weight is placed on the hinges, in contrast, particle board holds the screws in place under similar weight.  Product


Can refer to the additional process coating applied after electroplating and is the process of enhancing corrosion resistance of zinc and cadmium plated finished by conversion coating with usually a chromium bearing solution. 

Can also refer to a process for the surface treatment of stainless steels. Material is subjected to the action of an oxidizing solution, usually nitric acid, which augments and strengthens the normal protective oxide film enabling the material to resist corrosive attack. The passivating process also removes foreign substances from the surface which might cause local corrosion. 


The term used for nylon or adhesive locking coating on fastener threads.   Nylon    Adhesive


This is a nylon pellet inserted into a hole drilled in the fastener threads, in the UK the generic name is Wedglok.  Product


A bolt with a pentagon shaped head  Product


This is a brand of all metal prevailing torque locking nut. The nut is slotted in two places on the top after the nut has been tapped the slots, are bent slightly inwards and downwards. When the nut is screwed onto the bolt thread the two slotted parts are forced back to their original position. Their stiffness causes the nut threads to bind onto the bolt threads and provides prevailing torque locking.  Product


Phillips is a a type of screw drive that has a cross recess with a wide centre opening, steep walls and a blunt conical bottom. Permits easy and rapid entrance of the 4-winged driver.  more detail


Phosphate conversion coating is frequently added to bolt threads, to improve corrosion resistance. This type of chemical conversion coating provides a protective passivation layer.  Detail

Phosphating of drawing wire used to produce fasteners assists in lubricating the wire and facilitates cold forming.


Piles is a Term used in structural engineering for the joint plates.


A short piece of threaded taper or horizontal bar, Slotted, Square Head or Socket head, used to close up one end of a pipe fitting or drainage system.  Socket  Product


American Standard pipe threads are tapered 1 inch in 16 or 3/4 inch per foot. They are 60-degree threads, of National form with a flat or rounded top and bottom. 

British BSP for parallel and BSPT for tapered 

Metric taper threads show the pitch and then a T for Taper


The nominal distance between two adjacent thread roots or crests. In metric fasteners, the distance is measured in mm but for inch fasteners both American and British the threads per inch are counted.

The distance, measured parallel to its axis, between corresponding points on adjacent thread forms in the same axial plane and on the same side of the axis.  


On a straight thread, the diameter of the coaxial cylinder, the surface of which would pass through the thread profiles at such points as to make the width of the groove equal to one-half of the basic pitch. On a perfect thread, this occurs at the point where the widths of the thread and groove are equal.  


This term is applied to the finish of fasteners, is used to indicate that the fastener has had no supplementary surface treatment, such as plating and coating, other than being oiled. Sometimes referred to as self-colour.


Non-metallic fasteners made of a Nylon and other non-metallic materials that have a low dielectric constant and relatively high tensile strength, enabling it to resist high voltage at commercial frequencies. It can also operate at continuous temperatures as high as 120 degrees C.   Detail


Plating is the executing of a metallic deposit on the surface of the fastener by electrolysis, sometimes referred to as electroplating. Coating


Plough or Plow bolts have various shaped heads a square neck followed by a threaded portion.  Product


Pooching is a term sometimes used to describe the effect of the area immediately surrounding a tapped hole being raised up as a result of the tension from the stud. Tapped holes are often bored out for the first couple of threads to eliminate this problem.


Four-winged drive, with Pozidriv each slot is the result of two machining processes at right angles. The result of this is that the arms of the cross are parallel-sided. more detail


The tension created in a fastener when first tightened. Reduces after a period of time due to embedding and other factors.


The torque required to run a nut down a thread on certain types of nuts designed to resist vibration loosening. The resistance can be provided by a plastic insert, a non-circular head or deformed or coated threads.


A type of lock nut which has a prevailing torque to assist in preventing self-loosening. There are two main categories of prevailing torque nuts, all metal and nylon insert.

All metal torque prevailing nuts generally gain a prevailing torque by distorting the threads of the nut by some means. Aerotight, Anco, Binx, Cleveloc, Centre lock, Flexloc, Philidas, Snep, Staytite, Stover, Toplock and Vargal are all considered all metal locking nuts.

Nylon insert torque prevailing nuts utilise a nylon (or another polymer) insert to achieve a prevailing torque. The nylon insert nut family fit into this category both metric and Inch.


The proof load of a nut is the axially applied load the nut must withstand without thread stripping or rupture. The proof load of a bolt, screw or stud is the specified load the product must withstand without permanent set.

PROPERTY CLASS             

A designation system which defines the strength of a bolt or nut sometimes called the grade. For metric fasteners, property classes are designated by numbers where increasing numbers generally represent increasing tensile strengths. The designation symbol for bolts consists of two parts:  

The first numeral of a two-digit symbol or the first two numerals of a three-digit symbol approximates 1/100 of the minimum tensile strength in MPa.  

The last numeral approximates 1/10 of the ratio expressed as a percentage between minimum yield stress and minimum tensile stress.  

Fasteners with a property class of 8.8 have a minimum tensile strength of 800 MPa and a yield stress of 0.8x800=640 MPa.

The designation system for metric nuts is a single or double digit symbol. The numerals approximate 1/100 of the minimum tensile strength in MPa. For examples of nuts of property class 8 has a minimum tensile strength of 800 MPa. A bolt or screw of a particular property class should be assembled with the equivalent or higher property class of nut to ensure that thread stripping does not occur.


The amplification of an external force acting on a bolt by a lever action which can occur when that force is an eccentric tensile load.


Push nut is a generic term for Starlock ®  and similar brands of push on fastener for plain shafts. Push nuts eliminate costly threading and grooving operations, facilitate rapid assembly, and once fixed in position, are so secure that they cannot be removed without destruction.  Product






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