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alloy steel
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A type of steel that contains another material that is added intentionally to improve the properties of the metal.
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aluminum
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A silvery, white metal that is soft, light and is electrically and thermally conductive.
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bearing surface
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The circular underside of the bolt head that makes contact with the part.
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binding head
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A type of head that is similar to the pan head but much thicker with a deeper slot.
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bolt
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A cylindrically shaped, threaded device used for fastening parts. Bolts usually have blunt ends and mate with a nut.
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bolt stretch
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The amount of tension in a bolt after the wrench has been removed. Bolt stretch determines the strength of the bolted joint.
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bolted joint
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Two pieces of metal joined together by the use of threaded fasteners.
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brass
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A nonferrous alloy containing copper and zinc. Brass has high tensile strength and corrosion resistance.
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carbon steel
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A type of steel made up of iron and carbon and no other material. Most fasteners are made from carbon steel.
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carriage bolt
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A type of bolt with a round head and a square neck that prevents the bolt from turning while the nut is tightened.
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chamfer point
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A type of point that is similar to a pilot point. A chamfer point also has a truncated end to help the assembler guide the fastener into the hole.
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cheese head
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A type of head that is very thick allowing for a deep slot for increased driving power.
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clamping force
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The compressive force that a fastener exerts on a joint.
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clock system
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A system that identifies the strengths of nuts.
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cold working
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The shaping of metal at temperatures much lower than the metal's molten state.
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cone point
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A type of point with a cone shape that allows for deep penetration and is used for permanent location of parts
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conical washer
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A type of spring washer used with screws to increase the elastic properties of a joint.
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copper
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A reddish-brown metal that is very ductile, thermally and electrically conductive, and corrosion resistant. Copper fasteners are often used for electrical components.
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corrosion resistant
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The ability of a material to resist chemical destruction from an environment. Corrosion resistance is the most important physical property for fasteners.
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counter-bored hole
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A hole that has been enlarged to accept a bolt so that it can be seated flush with or below the surface.
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countersinking
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The cutting of a beveled edge at the end of a hole so that the head of a fastener can rest flush with the workpiece surface.
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cross threading
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A condition that occurs when a rotating fastener is misaligned with a tapped hole.
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dome-head bolt
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A type of bolt with a round head above the wrench flats.
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driving recess
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The shape on the top of a fastener head designed to accept a particular tool.
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electrical conductivity
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The ability of a material to conduct an electrical current.
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environmental resistance
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The ability of a fastener to resist forces in the environment that attempt to deform it.
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fastener
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A device that holds two or more objects together. A fastener can be a bolt or a screw as well as a button or a zipper.
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fastener diameter
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The distance between certain points on a fastener. Fastener diameter is measured using the shank, thread, and root of the fastener.
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fastener length
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A measurement of a fastener based on its head style. Generally, fastener length is measured from the underside of the head to the tip of the fastener.
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fastener type
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A category that indicates the function and design of a fastener. A wood screw is a fastener type categorized by the material it fastens.
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fatigue life
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The length of time a thread lasts before breaking down or failing.
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faying surfaces
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Two surfaces which lie close together or fit together.
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fillister head
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A type of head that is similar to the cheese head but with a rounded top for better appearance.
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flat head
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A type of head that is flat in shape and is used in countersunk holes.
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flat point
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A type of point with a blunt end used where parts must be frequently re-set.
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flat washer
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A type of washer that is slighly oversized allowing it to slide easily over the bolt.
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flat-head screw
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A type of screw that has a flat-shaped head style.
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Frearson
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A type of driving recess similar to Phillips but with less tapered slots.
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gimlet point
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A type of point with a sharp tip used for penetrating wood.
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grade
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A category, rank, or level of quality. Bolts are classified by grades.
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Grade 2
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An inch series strength grade that has no slash marks and is used for low-carbon steels.
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Grade 5
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An inch series strength grade that has three slash marks and is used for medium-carbon steels that have been quenched and tempered.
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Grade 8
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An inch series strength grade that has six slash marks and is used for alloy steels that have been quenched and tempered.
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grip length
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The length of the unthreaded portion of the bolt shank.
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head style
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The shape of the fastener head. There are many different head styles for fasteners.
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hex bolt
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A type of bolt that has a head with six sides.
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hex key
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A small, hexagonal-shaped wrench designed to be used with socket head cap screws.
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hex socket
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A type of driving recess with a hexagonal indentation designed to accept an Allen wrench.
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hexagonal head
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A type of head that has six sides. A hex head is the standard head style for machine bolts and screws.
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hex-washer head
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A type of head that is similar to the hex head except with a washer at the base.
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identification marking
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A marking on a fastener that often indicates the maker of the part and/or the manufactured fastener capability.
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lag bolt
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A heavy-duty wood screw that has a square or hexagonal head so they can be turned with a wrench.
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low-carbon steel
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A type of carbon steel that contains less than 0.3% carbon. Grade 2 fasteners are common low-carbon steel fasteners.
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major diameter
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Another name for thread diameter.
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material type
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A category that indicates the material from which a fastener is made as well as its grade. Carbon steel is the most common material type.
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medium-carbon steel
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A type of carbon steel that contains between 0.3% and .05% carbon. Grade 5 fasteners are common medium-carbon steel fasteners.
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megapascal
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The metric unit of pressure. Megapascal is abbreviated Mpa.
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minor diameter
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Another name for root diameter.
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nonferrous metal
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A metal that does not contain iron. Aluminum, copper, and zinc are nonferrous metals.
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oval head
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A type of head that is oval in shape and is used when appearance matters.
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oval point
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A type of point with an oval-shaped end used for frequent adjustment without deforming the part's bearing surface.
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pan head
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A type of head that is wide and provides great clamping strength. Pan heads are unattractive and are often used where they will not be seen.
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Phillips
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A type of driving recess that has an X-shaped indentation designed to accept a Phillips screwdriver.
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pilot point
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A type of point that has a truncated end to help the assembler guide the fastener into the hole.
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plow bolt
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A square-head bolt often used on heavy construction equipment.
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point style
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The shape of a fastener point. Point style controls the amount of material penetration or alignment.
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Pozidriv
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A type of driving recess that has an X-shaped indentation with a star-like shape on top designed to accept Pozidriv screwdrivers.
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proof load
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The tension-applied load that a fastener must support without evidence of deformation. Proof load is often used interchangeably with yield strength.
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property classes
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A designation system that defines the strength of metric fasteners. These designations consist of numbers where increasing numbers represent increasing tensile strengths.
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quenched
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The state of the cooling of metal rapidly by using water, air, or oil.
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radial line
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A line on the surface of a nut that extends out like a circle radius.
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Robertson
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A type of driving recess that has a square-shaped indentation designed to accept a special power-tool bit or screwdriver.
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root diameter
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The distance between the roots of a thread. Root diameter is the smallest diameter on a thread.
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round head
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A type of head that is round in shape and sits flush against a surface.
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screw
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A threaded device used for fastening parts or transferring motion. Screws usually have pointed ends.
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shank diameter
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The diameter that is measured on the shank of the fastener. Shank diameter is approximately the same as thread diameter.
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sheet metal screw
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A type of screw with a sharp, pointed end and sharp threads for penetrating sheet metal.
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size number
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A number assigned to indicate the measurement of a fastener's diameter.
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slotted
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A type of driving recess that has as straight-line slot designed to accept a flat-blade screwdriver.
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Society of Automotive Engineers
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An organization of engineers that sets most industry standards for the testing, measuring, and designing of automobiles and their components.
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socket head cap screw
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A type of cap screw with a round head and a hexagonal indentation for tightening purposes.
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stainless steel
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A type of steel that contains more than 15% chromium and exhibits excellent corrosion resistance.
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structural bolt
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A heavy type of hex bolt intended for use in large structures, such as buildings and bridges.
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tapped hole
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A type of hole that contains internal threads created by forming or cutting.
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tempered
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The state of the hardening of a metal by the use of heat treatment.
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tensile strength
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The ability of a material to resist forces that attempt to pull it apart or stretch it.
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thread diameter
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The distance between the crests of a thread. Thread diameter is the widest diameter on a thread.
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thread gage
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A measuring instrument used to inspect the internal threads of a part.
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thread pitch
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The distance from one thread groove to the next, measured from crest to crest.
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torque
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The amount of force applied to tighten a threaded fastener.
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Torx
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A type of driving recess that has a six-lobed indentation designed to accept Torx screwdrivers.
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truss head
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A type of head that is similar to the pan head but with a shallower head and rounded on top.
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twelve-point bolt
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A type of bolt with a double hexagon head. Twelve-point bolts are high-strength fasteners often used in the aircraft industry.
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washer
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A flat disc with a hole through the center that is often used with threaded fasteners to ensure joint tightness.
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weight-to-strength ratio
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The weight of an object divided by its strength. Twelve-point bolts have a low weight-to-strength ratio.
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wood screw
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A type of screw with a sharp, pointed end and a tapered shank with sharp threads for penetrating wood. Wood screws come in a variety of styles.
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wrench flats
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A flat surface beneath the fastener head that facilitates tightening with a wrench.
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yield strength
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The load at which a fastener experiences a specified amount of permanent deformation.
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