Glossary A.B.C

AMS Aeronautical Material Specifications    

Material and process specifications for aircraft components conforming to  recognised engineering and metallurgical practices in the aircraft industries. They are developed by the SAE aeronautics committee.   All specifications are prefixed by  "AMS" . AN Dimensional standards for aircraft fasteners developed by the Aeronautical Standards Group. All drawings are prefixed by "AN" ASTM Standards developed by the American Society for Testing and Materials.   

Acorn Die    

A form of threading die for use in screw machines. The cutting portion resembles an acorn.   

Acorn Nut    

A blind tapped hex nut with an acorn shaped top. Provides sealing for projecting threaded parts.  

Age Hardening   

A process of aging that increases hardness and strength, and ordinarily decreases ductility.  Age hardening usually follows rapid cooling or cold working.   

Air Force & Navy Aeronautical Standard Drawings    

Dimensional standards for aircraft fasteners developed by the Aeronautical Standards Group . All drawings are prefixed by "AN" .  

American Standards   

Dimensional standards for fasteners, etc., developed by the American Society of Mechanical Engineers. (ASME)   

Angle of Head    

In countersunk heads, the included angles of the conical underportion or bearing surface, usually 82 or 100 degrees.    



Used in  "quick release pins" where permanent assemble and disassemble action tales place. Provides a reliable holding fastener.  

Barrel Nut    

An internally threaded screw having a slotted head.   

Bent Bolt    

A cylindrical rod having a thread at one end and the other end bent to some desired conformation; also a bent cylindrical rod having threads at both ends.   


A surface not at right angles to the rest of the piece.   

Binding Head    

Rounded top surface and slightly tapered sides. The bearing surface is flat with annular undercut optional.  

Blind Rivet

A rivet designed for use where only one side of the work is accessible.   

Blunt Start    

The removal of the partial thread at the entering end of thread.   

Body of Bolt or Screw    

Also designated grip. The blank portion of the bolt or screw which is between the thread and the head.   

Bolt Blank    

A headed rod or bar intended for a subsequent threading operation.   

Bolt End    

A headless rod threaded at one end and assembled with a square nut, designed to be welded or otherwise fastened to a part or structure.   

Brinell Hardness Test    

A method of determining the hardness of metallic materials by applying a known load to the surface of the material through a hardened steel ball of known diameter. The diameter (or depth) of the resulting impression in the metal is measured. The Brinell hardness number is taken as a quotient of the applied load divided by the area of the surface impression which is assumed to be spherical.    


A generating process whereby metal is removed with a multiple-point tool, usually a bar, with tooth height increasing from the starting end. When the broach is pulled or pushed through or over the work, each tooth removes a clip of uniform thickness, in contrast to a milling cutting tooth which removes a wedge-shaped chip.    

Button Die    

Small adjustable dies for screw machines and similar work, supported in a ring holder.    


To smooth or polish by a rolling or sliding tool under pressure.     


Cap Nut    

A blind tapped hex nut with an acorn-shaped top. Provides sealing for projecting thread parts.    

Cap Screws    

Term used to describe hexagon head, slotted head, square head and socket head cap screws.    

Captive Screws    

Where the shank above the threaded portion is undercut lower than the threaded portion.    


A compound of carbon with one or more matallic elements.    

Carbide Tools    

Tools with cutting points of tungsten, tantalum or other alloys of sintered carbides.    

Carbon Steel    

Any steel made by combining carbon with iron.    

Carriage Bolts    

A round or flat head bolt with a square neck to prevent rotation. Used in wood assemblies.    

Case Harden    

Hardening a ferrous alloy so that the outer portion or case is made substantially harder than the inner portion or core. Typical processes used for case hardening are carburizing, cyaniding, carbonitriding, nitriding, induction hardening, and flame hardening.    


1. A term applied to the act of pouring molten metal into a mold.  

2. The metal object produced by such pouring.  

Castle Nut  

A hexagon nut having a cylindrical portion at the end opposite to the bearing face, with opposed slots in this portion which are parallel to the axis, designed for insertion of a cotter to secure the nut in place when used with a drilled fastener.    

Centerless Grinding    

Grinding the outside or inside diameter of a round piece not mounted on centers.    

Chamfer    (v) To bevel a sharp external edge. (n) A beveled edge.    

Chasing Threads    

Cutting screw threads by moving a tool along the axis of the work to be threaded.    


Rough or unsatisfactory surfaces on work. It is usually caused by a slight jumping of the tool away from the work or of the work away from the tool.    

Check Nut    

A double chamfered hexagon machine screw nut Class 3B fit. (AN 316).    


The metal removed by a tool.    


Device for holding work in machine tools.    

Class of Thread    

Class of threads are distringuished from each other by the amount of tolerance or tolerance and allowance specified. Classes 1A, 2A, and 3A apply to external threads, and Classes 1B, 2B and 3B apply to internal threads.    


U-shaped shackle for connecting a rod to a pin.  

Clevis Pins  

A headed dowel pin with a drilled shank that accepts a cotter pin. Used as a fastener where more than temporary holding actions is required. (ASA B 5.20-1958).  

Clinch Nut  

A nut having a pilot which, after insertion in a hole, is clinched or staked in place to prevent rotation.  

Cold Heading  

Forcing metal to flow cold into dies to form thicker sections and more or less intricate shapes. The operation is performed in specialized machines where the metal, in the form of a wire or bar stock, may be upset or headed in certain sections to a larger size and, if desired, may be extruded in other sections to a smaller diameter than the stock wire.  

Cold Swaging Process  

A method of reducing or forming steel or other material while cold, by drawing to a point or reducing the diameter, as may be required.  

Cold Work  

To deform metal stock by hammering, forming, drawing, etc., while the metal is at ordinary room temperature.  


A metal which may be added to chrome-nickel stainless steel to improve its welding and general heat-resistant qualities, by preventing carbide precipitation.  

Companion Flanges  

Shaft attached collars of 18-8 stainless steel into which a threaded piece may be joinedd. Has standard I.P.S. threads.  


A device for inspecting screw threads and outlines by comparing them with a greatly enlarged standard chart.  

Cone Point  

A point in the form of a cone, commonly having an included angle of 90 degrees or 118 degrees when applied to set screws. 

Copper Steel  

When any minimum copper content is specified, the steel is classed as copper steel. The copper is added to enhance errosion resistance of the steel.  


Gradual chemical or electrochemical attack on a metal by atmosphere, moisture or other agents.  

Cotter Pin  

Used as a locking device in clevis pins, castellated nuts and slotted nuts with drilled bolts. Ends available in various types such as "extended mitre end" , etc.  


(v) To enlarge a hole to a given depth. (n) 

1. The cylindrical enlargement of the end of a drilled or bored hole. 

2. A cutting tool for counterboring, having a piloted end of the size of the drilled hole.  

Countersunk Head

A head, the underside of which is beveled to fit a flaring hole. The bearing surface of other types of heads is generally perpendicular to the body axis.  


That surface of the thread which joins the flanks of the thread and is farthest from the cylinder or cone from which the thread projects.  

Crest Clearance  

As in a thread assembly, the distance, measured perpendicular to the axis, between the crest of a thread and the root of its mating thread.  

Crest Truncation of Thread  

The distance, measured perpendicular to the axis, between the sharp root and the cylinder or cone which bounds the root.  

Cup Point  

A point in the form of a cone, commonly having an included angle of 90 degrees, with a conical depression in the end commonly having an included angle of 118 degrees. The contact area is a circular ridge which has considerable holding power with slight penetration, applied to set screws generally.