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Glossary of terms for screws & fasteners
Use the links below to find important terms and their definitions
A | B | C | D | E | F | G| H | I | J | K | L | M | N| O | P| Q | R | S | T | U | V | W | X | Y| Z
Parts of a fastener
Angle of head. Specific to countersunk screws, this refers to the angle of the underside of the head. While 82° is considered the industry standard, 90° and 100°are also commonly used for specific applications.
Bearing surface. The area under the head of the fastener in contact with the fastened material.
Head. The part of the fastener by which it is installed. There are many head types but some of the most common are hex, countersunk, flange, and pancake heads.
Major diameter. The outside diameter of the threaded section of a screw.
Minor diameter. The diameter of the screw shank between threads.
Pitch. The distance between thread peaks.
Pitch diameter. The height of the threads, also defined as the difference between the major and minor diameters.
Powder coating. An alternative to liquid paint, powder coating is a process in which very fine particles of a colored media are electrostatically applied to a fastener. The fasteners are then baked at 350–450 degrees Fahrenheit to melt and cure the powder, providing a long-lasting and durable coating.
Shank. The unthreaded section of a fastener. Typically seen on long length fasteners.
Threads. A triangular-shaped profile that wraps around the fastener following the curve of a helix.Fastener materials
Alloy steel. A combination of carbon steel and other metals that enhances the material’s mechanical properties, making it more suitable for specific applications. Alloy steels are generally considered affordable and easily accessible.
Carbon steel. Steel with a relatively high carbon content making it suitable for heat treatment. However, this makes the steel less malleable and increasingly vulnerable to corrosion if not protected.
Stainless steel. An alloy of iron, carbon, chromium, and nickel, stainless steel is widely used for its corrosion resistance. Its strength and ability to combat corrosion in rigorous environments have made it incredibly popular for premium fasteners. However, it's one of the more expensive metals. It can also be susceptible to the damaging effects of extreme temperatures.
Zinc. A metal which, for fasteners, is most commonly used as an exterior coating to limit the damaging effects of moisture and acidic environments. An example of fasteners that utilize zinc for its rust-resistance properties are ZAC® Impax™ screws.
Fastener manufacturing
Cold forming. A manufacturing process in which metals are formed at room temperature using high pressure to form the material. When producing large quantities, it is considered the more affordable alternative to hot forging.
Cut threading. A fastener manufacturing process in which excess metal is removed from the blank diameter to form the threads.
Die. A tool used to form the geometry of the fastener eg. head, threads, point.
Hot forging. A manufacturing procedure in which metal is heated to extreme temperatures before forming. Hot forging accommodates a wider variety of metals and design needs than cold forming.
Roll threading. Distinctly different from cut threading, roll threading is a type of cold forming manufacturing process in which a die rolls the blank part across another die at high pressures, forming the raw material into the voids, which creates the thread geometry.
Wire drawing. A cold forming metalworking process in which a solid steel wire passes through a circular die to reduce the diameter to the desired size. Wire drawing can change the mechanical properties of the material.
Fastener silhouette and design
Coarse threads. When compared to fine thread screws, coarse thread screws have a larger pitch and more defined threads. Typically used on wood screws to optimize holding strength.
Countersunk. A low-profile screw head intended to be the same height as the surrounding surface (or shorter) when installed.
Fine threads. A screw design that features a higher thread count compared to its coarse thread counterparts. Typically used on steel attachment applications.
Flange head. A fastener manufactured with a flange around the head that acts similarly to a washer. The benefit of this is to disperse force across a larger surface area, increasing pull-over strength.
Hardened. Indicates that the manufacturer heat treated the fastener to increase mechanical properties such as tensile and shear strength.
Hex head. A screw head characterized by its hexagonal shape. Hex head fasteners are one of the most commonly used because of their ease of installation and universally accepted drive bit.
Knurl. A ribbed profile on the shank/thread transition; typically seen on wood screws to help reduce installation torque.
Low profile. Any screw head with minimized height to reduce visibility or increase clearance in tight spaces.
Pan head. A round flat screw head typically used in standing seam clip attachment applications where the fastener head will be covered with another panel.
Pancake head. Low profile screw head design that typically caps shorter fasteners. The profile supports the application needs of panels and timber.
Thread forming screw. A classification of screws in which the fastener forms threads in the mated material (common plastic or metal).
Truss head (mushroom head). A type of screw head with a wide, low-profile dome shaped head. This type of head is useful in applications with high clamping forces and pull-through is of concern.
Wafer head. Low profile screw head commonly associated with self-drilling fasteners. The flat, countersunk design makes them visually discreet.
Fastener conditions and measurements
Engagement. The length of the fastener which will be embedded into the substrate.
Fatigue. The compromising of a fastener’s or material’s structural integrity due to fluctuating loads.
Galvanic corrosion. The electrochemical phenomenon in which corrosion caused by exposure to moisture is expedited by the presence of differing metals. Commonly, one metal will rust significantly faster than the other which will, in turn, corrode slower than it would normally. Galvanic corrosion can be significantly slowed through specialized insulation.
Seizing (galling). When an active screw cannot turn due to adhesive wear of metal-on-metal friction. This can lead to the screw breaking during tightening. Seizing can also make loosening difficult.
Shear strength. The amount of force a fastener can tolerate perpendicular to the shank before failure, commonly estimated to be two-thirds of the measured Tensile Strength.
Stress corrosion cracking (SCC). The subsequent cracking that results from the combination of excessive load-bearing and high-corrosive environments. Examples of common catalysts for SCC include hydrogen-sulfide or chloride. Metals that have above-average resistance to SCC are stainless steel and bronze.
Tensile strength. The maximum force applied parallel to the length of a fastener can withstand without breaking. Commonly confused with Yield Strength.
Torque (torsion strength). The maximum rotational force which can be applied to the fastener before failure.
Yield strength. The maximum force a fastener can support before experiencing plastic deformation and compromising its hold. Commonly confused with Tensile Strength.
Search by alphabet
A
Alloy steel. A combination of carbon steel and other metals that enhance the material’s mechanical properties, making it more suitable for specific applications. Alloy steels are generally considered affordable and easily accessible.
Aluminum. The most pervasive of all the metals, aluminum is characterized by its balance of lightness, strength, and pliancy. Manufacturers choose it for its affordability, corrosion resistance, and ability to be recycled.
Angle of head. Specific to countersunk screws, this refers to the angle of the underside of the head. While 82° is considered the industry standard, 90° and 100°are also commonly used for specific applications.
B
Bearing surface. The area under the head of the fastener that is in contact with the fastened material.
C
Carbon steel. Steel with a relatively high carbon content making it suitable for heat treatment. However, this makes the steel less malleable and increasingly vulnerable to corrosion if it’s not protected.
Chrome (chromium plating). A metal commonly applied to the exterior of fasteners and parts for its protective hardness and corrosion-resistant properties.
Cold forming. A manufacturing process in which metals are formed at room temperature using high pressure to form the material. When producing large quantities, it is considered the more affordable alternative to hot forging.
Coarse threads. Compared to fine thread screws, coarse thread screws have a larger pitch and more defined threads. Typically used on wood screws to optimize holding strength.
Countersunk. A low-profile screw head intended to be the same height as the surrounding surface (or shorter) when installed.
Cut threading. A fastener manufacturing process in which excess metal is removed from the blank diameter to form the threads.
D
Die. A tool used to form the geometry of the fastener eg. head, threads, point.
E
Engagement. The length of the fastener which will be embedded into the substrate.
F
Fatigue. The compromising of a fastener’s or material’s structural integrity due to fluctuating loads.
Fine threads. A screw design that features a higher thread count compared to its coarse thread counterparts. Typically used on steel attachment applications.
Flange head. A fastener manufactured with a flange around the head that acts similarly to a washer. The benefit of this is to disperse force across a larger surface area, increasing pull-over strength.
G
Galvanic corrosion. The electrochemical phenomenon in which corrosion caused by exposure to moisture is expedited by the presence of differing metals. Commonly, one metal will rust significantly faster than the other which will, in turn, corrode slower than it would normally. Galvanic corrosion can be significantly slowed through specialized insulation.
Grip. The unthreaded part of a fastener.
H
Hardened. Indicates that the manufacturer heat treated the fastener to increase mechanical properties such as tensile and shear strength.
Hex head. A screw head characterized by its hexagonal shape. Hex head fasteners are one of the most commonly used because of their ease of installation and universally accepted drive bit.
Hot forging. A manufacturing procedure in which metal is heated to extreme temperatures before forming. Hot forging accommodates a wider variety of metals and design needs than cold forming.
I
ISO. Short-hand for International Organization of Standardization
J
K
Knurl. A ribbed profile on the shank/thread transition; typically seen on wood screws to help reduce installation torque.
L
Lead. The distance traveled by the exterior point of a screw (the threads) with one full rotation.
Low profile. Any screw head with minimized height to reduce visibility or increase clearance in tight spaces.
M
Major diameter. The outside diameter of the threaded section of a screw.
Minor diameter. The diameter of the screw between threads.
N
Nickel. A metal commonly used to enrich stainless steel to enhance corrosion resistance and strength in extreme temperatures.
O
P
Pan head. A round flat screw head typically used in standing seam clip attachment applications where the fastener head will be covered with another panel.
Pancake head. Low profile screw head design that typically caps shorter fasteners. The profile supports the application needs of panels and timber.
Pitch. The distance between the threads’ peaks, most commonly measured with millimeters.
Pitch diameter. The height of the threads, also defined as the difference between the major and minor diameters.
Powder coating. An alternative to liquid paint, powder coating is a process in which very fine particles of a colored media are electrostatically applied to a fastener. The fasteners are then baked at 350–450 degrees Fahrenheit to melt and cure the powder, providing a long-lasting and durable coating.
Q
R
Roll threading. Distinctly different from cut threading, roll threading is a type of cold forming manufacturing process in which a die rolls the blank part across another die at high pressures, forming the raw material into the voids, which creates the thread geometry.
S
Seizing (galling). When an active screw cannot turn due to adhesive wear of metal-on-metal friction. This can lead to the screw breaking during tightening. Seizing can also make loosening difficult.
Shank. The unthreaded section of a fastener. Typically seen on long length fasteners.
Shear strength. The amount of force a fastener can tolerate perpendicular to the shank before failure, commonly estimated to be two-thirds of the measured Tensile Strength.
Stainless steel. An alloy of iron, carbon, chromium, and nickel, stainless steel is widely used for its corrosion resistance. Its strength and ability to combat corrosion in rigorous environments have made it incredibly popular for premium fasteners. However, it's one of the more expensive metals. It can also be susceptible to the damaging effects of extreme temperatures.
Stress corrosion cracking (SCC). The subsequent cracking that results from the combination of excessive load-bearing and high-corrosive environments. Examples of common catalysts for SCC include hydrogen-sulfide or chloride. Metals that have above-average resistance to SCC are stainless steel and bronze.
T
Tensile strength. The maximum force applied parallel to the length of a fastener can withstand without breaking. Commonly confused with Yield Strength.
Thread forming screw. A classification of screws in which the fastener forms threads in the mated material (common plastic or metal).
Threads. A triangular-shaped profile that wraps around the fastener following the curve of a helix.
Torque (torsion strength). The maximum rotational force which can be applied to the fastener before failure.
Truss head (mushroom head). A type of screw head with a wide, low-profile dome shaped head. This type of head is useful in applications with high clamping forces and pull-through is of concern.
U
V
W
Wafer head. Low-profile screw head commonly associated with self-drilling fasteners. The flat, countersunk design makes them visually discreet.
Wire drawing. A cold forming metalworking process in which a solid steel wire passes through a circular die to reduce the diameter to the desired size. Wire drawing can change the mechanical properties of the material.
X
Y
Yield strength. The maximum force a fastener can support before experiencing plastic deformation and compromising its hold. Commonly confused with Tensile Strength.
