F... Glossary of Fastener and Fixing Terminology
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GLOSSARY ALPHA LOCATOR
FAN DISC LOCKING WASHERS
A serrated locking washer with a similar locking mechanism to a shakeproof washer. Product
FERRY BOLTS
Bolt or screw whose cross section of its head is in the shape of a 12 pointed star, also called 12 point bolts and Ferry bolts. Product
FILLISTER HEAD
The Fillister head (USA), or Raised Cheese Head. Product
FINE PITCH
Threads where the pitch is narrower than a coarse pitch. Metric Fine, BSF British Standard Fine, UNF American Unified Fine Detail
Fit is the general term used to signify the range of tolerance parameters. In effect the criteria for allowances and tolerances in the design of mating parts.
The Class of Fit is a measure of the degree of fit between mating internal and external threads. Three main Classes of Fit are defined for metric screw threads :
FINE: This has a tolerance class of 5H for internal threads and 4h for external threads.
MEDIUM: This has a tolerance class of 6H for internal threads and 6g for external threads.
COARSE: This has a tolerance class of 7H for internal threads and 8g for external threads.
For Unified threads, a similar designation as for metric threads is used. The thread classes used are 1A lose, 2A standard and 3A fine for external threads and 1B, 2B and 3B for internal threads.
FLANGE BOLT
Flange bolts have a washer flange as an integral part of the head removing the need for a washer and speeding up assembly time. Product
FLAT HEAD
Flat head is an American term for a Countersunk screw Product
FLEX LOC ® NUTS
The locking threads of the slotted top press inward against the bolt, lifting the nut upward and causing the remaining threads to bear against the lower surface of the bolt threads. Product
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.
FORGING
Forging is the process of forming a product by hammering or the displacement of material under force. When the material is forged below the re-crystallisation temperature it is said to be cold forged. When worked above the re-crystallisation temperature having been pre-heated, it said to have been hot forged. more detail Cold Hot
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.
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.
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