Glossary of Fastener Terminology

F

Facing: Facing is a machining operation on the end, flat face or shoulder of a fastener.

Fatigue Strength: Under variations in applied stress a fastener feels internal stretching that can cause rupture after a specific number of cycles. The number of cycles to failure for a specific load is the fatigue life of the screw. In rigid assemblies preloading above the external load should eliminate fatigue failure.

Ferrous: Relating to or containing iron.

Fillet: A fillet is the concave junction at two intersecting surfaces of a fastener.

Underhead Fillet: An underhead fillet is the fillet at the junction of the head and shank of a headed fastener.

Fin: A fin is a form of key under the head of a fastener which serves to keep the fastener from turning during assembly and use.

Finish: The term finish is commonly applied to the condition of the surface of a fastener as a result of chemical or organic treatment subsequent to fabrication. The term finish is also applied to some types of fasteners to indicate the condition of the surface as a result of mechanical operations and the degree of precision.

Finish Fastener: A finished fastener is a fastener made to close tolerances and having surfaces other than the threads and bearing surface finished to provide a general high grade appearance.

Fit: Fit is the general term used to signify the range of tightness which may result from the application of a specific combination of allowances and tolerances in the design of mating parts.

Flash: Flash is the thin fin of metal along the sides or around the edges of a forged or upset section. It is caused when metal flows out between the edges of the forging dies.

Flash Plating: Flash plating is a very thin deposit of metal, usually on the order of 0.00005 to 0.0001 5 inch in thickness.

Floating Type Flange Joint: A conventional flanged joint in which a gasket is compressed by bolts - the gasket is not rigidly located. Calculation methods such as the ASME code in the USA and the EN1591 code in Europe.

Fluoro-Carbon Thread Coating: A low friction coating applied to threads. This type of coating is frequently used to prevent thread fouling when an assembly containing threaded fasteners is painted. Unless masked in some way before painting, electro deposited primers can cover the threads. If this occurs assembly difficulties can result unless the expensive chore of cleaning the threads is completed. A fluoro-carbon thread coating eliminates the need for masking or cleaning since paint will not adhere to the coating. This type of coating can also prevent problems caused by weld splatter obstructing the threads of weld nuts during their placement. Such coatings also have the property of reducing the torque-tension scatter during tightening.

Following Flank: The flank of a thread opposite to the leading flank.

Forging: Forging is the process of forming a product by hammering or pressing. When the material is forged below the re-crystallization temperature it is said to be cold forged. When worked above the re-crystallization temperature it is said to be hot forged.

Form of Thread: The profile of a thread in an axial plane for a length of one pitch.

Friction: Mechanical resistance to the relative movement of two surfaces. There are two main types of friction; STATIC FRICTION and DYNAMIC FRICTION. Typically static friction is greater than dynamic friction.

Friction Stabilizers: Coating materials used on fasteners with the intention of reducing the scatter in the thread and bearing surface friction coefficients.

Full or Nominal Diameter Body: A full or nominal diameter body is a body the diameter of which is generally within the dimensional limits of the major diameter of the thread. Sometimes referred to as “full size body.”

Fundamental Deviation: An intentional clearance between internal or external thread and the design form of the thread when the thread form is on it's maximum metal condition. For metric threads the fundamental deviation are designated by letters, capitals for internal threads and small letters for external threads. Some tolerance classes have a fundamental deviation of zero. For imperial threads the fundamental deviation is called the allowance.

Fundamental Triangle Height: The fundamental triangle height is normally designated with the letter H. This is the height of the thread when the profile is extended to a sharp vee form. For 60 degree thread forms such as metric and Unified thread series, H equals 0.866025 times the thread pitch.

(Click on the letters below to browse the glossary terms)

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