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Glossary

Type A – Typically refers to standard sheet metal screw points. Sharp point, fewer threads and deeper than a type “AB” sheet metal screw. A standard off the shelf sheet metal screw in 18-8, some 316ss and carbon steel.

Type AB – Sharp point, finer thread than a type “A”, thread dimensions similar to a type “B” sheet metal screw. Not a common thread in stainless steel, but is available as a special.

AN – Stands for Army/Navy. AN Bolts, AN Washers, AN Screws

ANSI – American National Standards Institute

ASME – American Society of Mechanical Engineers.

ANSI/ASME – Typical standards for fasteners and related products. ANSI B18.3 Socket Heads, ANSI B18.2.1 Hex Heads, ANSI B18.6.3 Nuts, ANSI B18.2.2 Nuts, etc.

ASTM – American Society for Testing and Materials. ASTM A193 Hex Heads, ASTM A194 Hex Nuts, etc. ASTM F593 Hex Heads, ASTM F594 Hex Nuts

Age Harden – To use heat treatment methods over time to increase material strengths.

Anneal – To use heat treatment methods to reduce material hardness.

Austenitic - or 300 series, stainless steels make up over 70% of total stainless steel production. They contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from the cryogenic region to the melting point of the alloy. Typical stainless steel nuts and bolts are made from 18-8 stainless. Other variations are 302, 303, 304, 316, 304L, 316L, 302HQ, XM-7. This type of stainless is used in industries such as dairy, wine, chemical, pulp and paper, pharmaceutical, boating, medical and many more.

Type B – Refers to sheet metal screws with a blunt point and more threads per inch then a typical type A sheet metal screw.

Bearing Surface – The part of fasteners that comes in contact with the bolted joint it is being used on.

Binding Head – A low profile head, typical and a slotted drive style and Phillips on special order.

Broach – usually refers to a manufacturing style of using sharp edges to cut material and push it away. Broached fasteners would be socket heads, button heads, etc. Most are cold headed while larger size fasteners are “broached”.

Captive/Captivated – A term for a fastener that has a “captive” area under the head, usually at or below the minor diameter of the threaded area at the end of the screw. Captive fasteners are very common in the medical and electronic industry.

Certificate of Compliance/COC – certification stating that parts meet all required specifications it is being sold under.

Chromium – Chromium is the most important element in providing corrosion resistance in stainless steel. By adding 12% chromium to ordinary steel, stainless steel is formed. Chromium offsets the corrosive effects of carbon found in steel and is the primary factor in the ability of the stainless to form a passive film on its surface providing corrosion resistance.

Cold Forming – Cold Heading – Cold Working – When fasteners are produce without heating or small heat levels below the re-crystallization temp by pressing metal wire against various dies at a high speed to form a fasteners head and shape. Cold working causes an increase tensile strength and hardness and a decrease in ductility.

Copper – An excellent conductor of heat and electricity. It is malleable, ductile and nonmagnetic with low to average strength and good corrosion resistance. Brass and silicon bronze are composed mainly of copper and gain their strength from the addition of other metals such as silicon.

Cut Thread – Forming threads on a fastener by cutting material away.

Discontinuities – Small or large disfigurations in a fasteners such as pits, tool marks, voids, laps, folds, etc. Minor discontinuities are typically allowed, major as defined by various military specifications, MS, AN, NAS, NASM, etc.

Drawing – A term used in cold heading when pulling wire into the machine to cold form the screw heads. Also used to “draw” wire down from larger diameters to increase the strength.

Ductility – The ability of a fastener, screw, bolt to deform before breaking. Similar to elongation.

18-8 – Over the years this term has come to encompass 302, 302HQ, 303, 304, 305 and XM 7 stainless types. There is little overall difference in corrosion resistance among the 18-8 types, but slight differences do make certain grades more resistant to corrosion. 302 stainless, 302HQ (XM-7) and 304 are typically used in the cold heading process while 303 is used for screw machined parts. 18-8 is generally non-magnetic and is hardenable only by cold working.

Elongation – The stretching of a fastener or material to the breaking point. The percent of elongation at rupture is determined by dividing the total length after stretching to the original length. Typically decreases as strength and hardness increase.

Fatigue Strength – Measures the endurance of a fastener by showing what load it can accept without breakage under repeated loading cycles.

Ferritic – Ferritic stainless steels contain no nickel but have a higher chromium content providing greater corrosion resistance than martensitic stainless but much less than austenitic stainless. 400 series stainless usually make up this group, 410, 420, 431, etc.

Fit - A term typically used for thread fit of which there are many times. 1A, 2A, 3A, 1B, 2B, 3B along with UNC, UNF, UNJ, UJR etc.

Full Body Diameter – When the unthread portion of a fastener has the same major diameter of the threaded fastener area.

Galling – When two screws/fasteners stick together and cannot be easily loosened. when tightening fasteners a pressure builds on the threads as the metals rub against each other and the passive film preventing corrosion on stainless may not form due to lack of oxygen. Heat contributes to galling caused by high speed fastener installation. Thread lubrication is the best preventative and OSS offers many plating solutions such as dry film lube, nickel PTFE coating, PTFE coatings and many more.

Galvanic Corrosion – accelerated corrosion occurring when two different metals are in contact with moisture. All metals have a specific electric potential so that low level electric current flows from one metal to another. A metal with a high position in the galvanic series will corrode sacrificially rather than one with a lower position. Stainless steel will corrode before gold, etc. The further the metals are apart on the chart the more current will flow and the more corrosion will occur. Various plating’s and coating can be applied to fasteners to prevent this problem.

Grip/Grip Length – The unthreaded portion of a fastener. No to be confused as a shoulder or shoulder bolt.

Hardness – Measured in terms of Rockwell or Brinell. Shows resistance of a fastener to rough marks and abrasions. Also can indicate yield/tensile and brittleness of a fastener. However, for stainless the correlation between hardness and tensile, yield is tenuous with no defined correlation.

Heat Number/Heat Lot – This number is generated from the mills that melt the raw material used in screws/nuts/bolts. This number follows the fastener through its life cycle and traces back to the raw material melt source.

Heat Treat/Heat Treatment – Heating often combined with cooling and annealing to achieve a higher strength fastener. Some stainless, 410, 420, 440 and materials like 17-4, 15-7, A286, 718, 625 etc. are heat treated to obtain higher strength fasteners.

Hot Forging – Typical for large size fasteners and exotic metal fasteners such as A286, Alloys 600, 625 and 718. Heating metal bar to high temperature and shaping the fastener head style with a press. Also used in time when a small quantity of fasteners are needed.

Hydrogen Embrittlement – Hydrogen trapped under the surface of a plated fastener can later cause failure in the fastener. It is typically associated with alloy steels and not stainless fasteners. There may be no external signs of corrosion before a break occurs. Parts are typically baked for 3 to 24 hours depending on hardness to relieve the potential for embrittlement.

IFI – Industrial Fastener Institute.

In Process Sampling – SPC – a typical production inspection technique in which an pre-determined number of random samples is pulled from the production line and dimensionally inspected or mechanically if required.

Jam Nut – Slightly thinner than a regular hex nut. Used in pairs to “jam” together for a locking effect.

Liquid Penetrant Inspection – A test method for finding cracks and discontinuities in fasteners. Parts are dipped in dye and inspected under ultraviolet light. Typical on aerospace fasteners and fasteners that will see high loads.

Lot Number/Lot – A way of tracking batches of fasteners. All parts at OSS have lot traceability back to the source and in most cases back to the raw material heat number.

Lot Sampling – This is a random sampling of parts from any given lot for dimensional inspection. There are certain standard which can dictate this or customer requirements can dictate this. OSS uses ANSI/ASQC Z.14 AQL 1.0.

MS – Military Standard. OSS carry’s a wide variety of MS style fasteners and products. These specs guarantee physical and mechanical quality and are traceable back to the raw material and testing certifications. In recent years these have been replace by “NASM” specifications, but are interchangeable.

Machinability – Same as free machining. Refers to the malleable characteristics of metal when cutting or forming on screw machines.

Magnetism – 300 series stainless is non-magnetic in its raw material form. Depending on the actual chemical makeup and cold working, magnetism can be present. This rise in magnetism is related to an increase in tensile strength and work hardening caused by the heat and friction of cold forming and does not reduce corrosion resistance or cause any molecular change in austenitic raw material.

Magnetic Permeability – A test to determine the level of magnetism. Air = 1.0, most stainless fasteners are required to be 2.0 or less.

Major Diameter – largest or outside diameter of the screw threads.<\

Manganese – A non-magnetic metal which can improve strength and hardness in a fastener.

Martensitic – Martensitic refers mainly to stainless types 410, 416 and 420. Named for Robert Martens, these grades have a high carbon content which reduces corrosion resistance but allows a sharp increase in tensile strength after heat treatment. Martensitic stainless is magnetic, contains no nickel and loses toughness in very cold temperatures. Its corrosion resistance is not as good as austenitic or ferritic stainless so these types of fasteners are used in mild atmospheres.

Minor Diameter – The smallest diameter of a screw thread.

Molybdenum – Also known as Moly. The metal is added to 316 stainless steel to sharply increase its corrosion resistance to chlorides and sulfates and various acids used in the pulp industry. Moly helps to reduce hardness and increase tensile strength at higher temperatures.

Monel® - The trade name given to Nickel Copper (NiCu) and invented by International Nickel Co. This is basically two thirds nickel and one part copper. Fasteners, screws and nuts made from this material has good strength, excellent corrosion resistance against salt water and in high temperatures.

NAS – National Aerospace Standards. OSS carry’s a wide variety of NAS bolt, NAS nut, NAS washer style fasteners and products. These specs guarantee physical and mechanical quality and are traceable back to the raw material and testing certifications.

Nickel – A metal added to 300 series stainless to provide corrosion resistance, increased strength at both high and low temperatures. Nickel lowers the effects of work hardening thus helping to reduce the magnetism that can occur from cold forming.

Non-Ferrous – Metals without iron. Brass and silicon bronze are non-ferrous. Stainless and other corrosion resistant fasteners are typically characterized as non-ferrous, but that is actually incorrect since a major component is in fact iron.

Nylon – Light weight, low in strength but has great resistance to many chemicals and is good for insulation.

Passivate/Passivating – This can be a very confusing term. There are two sides of it, the mil-spec side and commercial fastener side. On the mil-spec side, passivation is a process that dips the fasteners into a nitric acid solution to rapidly form a chromium oxide on the surface of the material creating a passive film that protects the stainless from further oxidation. QQ-P-35 later replaced by AMS2700 is the most common specification used. On the commercial side the term is a little more generic. The purpose is to remove both grease left from manufacturing and traces of steel particles which may have rubbed off in the manufacturing process.

Passive Film – The major characteristic of stainless is its ability to form a thin layer of protection called a passive film on its outside surface. This film results from a continual process of low-level oxidation, so oxygen from the atmosphere is needed for the passive film to exist. Once formed, it prevents further oxidation/corrosion from forming.

Pitch/Thread Pitch – The distance between two adjacent threads measured at the outside diameter of the threads.

Proof Load/Tensile Strength – A test load on a fastener. It is the load needed to pull a fastener apart.

Roll Threading – A typical style of forming threads on fasteners. Parts start out at pitch diameter and are “rolled” thru a set of dies to form the threads. This style moves the grains of material instead of removing the grain like a cut thread would. The roll threading also work hardens the material resulting in a stronger fastener.

Shear Strength – Measured by push or pull against the side of a bolt, fastener, until the fastener breaks. As a rule, shear strength is two thirds of the tensile strength. Double shear is another testing method in which for is applied in two places on the fastener.

Silicon – A non-metallic substance that adds strength and toughness to copper to help for a bronze alloy.

Silicon Bronze – Alloy consisting of 95-98% copper plus a small amount of silicon added for strength. Silicon bronze is non-magnetic with a high degree of thermal conductivity and high corrosion resistance against sea water, gases and sewage.

Stainless Steel – With the addition of chromium to iron, stainless steel is formed. The chromium protects the iron against most corrosion or rust, thus the term stainless steel. The ability of stainless to form a thin layer of protection on its outside surface, called a passive film, is its moth important characteristic in preventing corrosion. Also see Austenitic, Martensitic, Ferritic.

Stamping – A manufacturing method used to make washers and various parts out of sheet.

Strain Hardened – To increase hardness and strength by cold working of raw material or cold forming a fastener. The standards are various and numerous for different materials.

Tantalum – A gray ductile metal with a high melting point and excellent corrosion resistance against chemicals.

Tap Bolt – A fully threaded fastener, typically hex head cap screws.

Temper – To heat material after hardening to a temperature and allow it to cool naturally in order to soften material and make it less brittle. Also to heat to a lower temp to relieve stress in metal without affecting the hardness.

Tensile Strength - The load needed to pull a fastener apart.

Titanium – A silver gray metal with high corrosion resistance against salt waters, chlorides and many acids. It is strong and lightweight.

Work Harden – An increased level of hardness caused by cold forming fasteners.

Yield – The resistance to a load pulling on the middle of a fastener until the fastener shows permanent deformation.

More articles from OSS:

From Cutlery to Space Shuttles: The History of Stainless Steel and Superalloys

The History of the U.S. Fastener Industry

An Introduction to Superalloys

A Strong Family Tree: An Introduction to the Grades and Types of Stainless Steel

The ABC's of Nuts and Bolts

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