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12-UN series
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A standard diameter-pitch combination with medium-pitch threads and 12 threads per inch. This series is commonly used instead of UNF threads for bolt diameters over 1 1/2 inch.
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16-UN series
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A standard diameter-pitch combination with fine-pitch threads and 16 threads per inch. This series is also used for fine threads with bolt diameters over 1 3/4 inch.
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8-UN series
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A standard diameter-pitch combination with coarse-pitch threads and 8 threads per inch. This series is commonly used instead of UNC threads for bolt diameters over 1 inch.
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adhesive bonding
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The joining of two or more materials through the use of adhesives such as liquids, drops, or gels.
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allowance
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A specific amount of clearance or interference between threads.
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asymmetrical
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Having sides that are different. A buttress thread has asymmetrical sides.
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blind threaded hole
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A type of hole that does not go completely through the material. Most screws are assembled into blind threaded holes.
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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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buttress thread
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A thread with an asymmetrical ridge that has one straight and one angled flank.
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chip
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An unwanted piece of metal that is removed from a workpiece. Chips are formed when a tool cuts or grinds metal.
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class of fit
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A system that designates how loose or tight the thread should be in general.
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clearance
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An amount of space or distance between two objects.
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cold forming
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The shaping of a metal at room temperature.
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crest
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The top where two flanks meet on a thread.
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cutting tool
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A device made of hard, tough material that is used to remove metal by creating chips.
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cylinder
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A solid, three-dimensional shape with circular ends and straight sides.
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depth
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The length of the space measured from the base of the root to an imaginary line spanning the crests of a thread.
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diameter
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The distance between certain points on a thread.
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double-start thread
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Having two ridges wrapped around the cylinder.
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driver adaptor
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A torque sensor that connects to a computer interface. A driver adaptor is a device that expands the range of the tool.
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external thread
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A type of thread formed on the outside of a cylinder, such as on bolts and screws.
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fastener
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A device that holds two or more objects together. A fastener is a bolt or a screw, or even a button or a zipper.
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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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fatigue resistant
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Opposition to breaking down or failing from use.
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female thread
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Another name for internal thread.
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flank
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An angled side of the body of a thread that connects the root to the crest.
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head
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The top of a fastener. Different types of fasteners have differently shaped heads.
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helical
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Winding around in a spiral, spring, or coil.
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helix
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A spiral structure that contains a repeating pattern.
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included angle
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The angle created by two adjacent flanks.
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inside diameter
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The interior surface of a spherical or cylindrical object.
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interference fit
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An amount of overlap between two objects.
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internal thread
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A type of thread formed in holes, such as in nuts.
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International Organization for Standardization
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An organization based in Switzerland that develops and publishes standards for its international membership base. It is often referred to as ISO.
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ISO metric thread
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A standard thread form based on millimeters that was developed for use in Europe.
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lead
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The distance that a screw travels in one revolution.
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left-hand thread
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A type of thread that is screwed in by rotating it counterclockwise. Left-hand threads are rare.
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major diameter
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The distance between the crests of a thread. Major diameter is the widest diameter on a thread.
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male thread
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Another name for external thread.
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metric designation
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The letter "M" that is at the beginning of all metric thread designations.
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metric thread standard
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A thread made to a scale that is based on millimeters.
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minor diameter
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The distance between the roots of a thread. Minor diameter is the smallest diameter on a thread.
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nominal diameter
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The overall diameter of the part. Nominal diameter is one of the parts of a metric thread specification.
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nominal size
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The size by which something is known, which may be different from its actual, measurable size. A wooden 2 x 4 is actually 1 3/4 x 3 3/4 inches.
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non-threaded fastener
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A type of fastener that does not contain threads.
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nut
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A block, usually of metal, with a threaded hole that mates with a bolt. The outer shape of a nut is often six-sided.
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outer diameter
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The exterior surface of a spherical or cylindrical object.
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pitch
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The distance from one thread groove to the next measured from crest to crest.
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pitch diameter
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The measured distance between the pitch points taken in the groove between the threads. Pitch diameter is one of the most important dimensions in thread inspection.
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pitch point
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The position on the thread where an equal amount of distance exists between the flanks on the solid part of the thread and in the space between the threads.
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rail feeder
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A screw feeding machine.
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right-hand thread
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A type of thread that is screwed in by rotating it clockwise. Most fasteners have right-hand threads.
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root
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The base where two flanks meet on a thread.
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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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single-start thread
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Having one ridge wrapped around the cylinder.
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square thread
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A thread with box-like ridges. The crests are at 90° angles from the flanks.
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start
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The number of individual threads on a device.
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stress area
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The area of a thread that is subjected to a tensile force.
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symmetrical
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Having similarity in size, shape, and position. A V-shaped thread has symmetrical flanks.
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tensile stress area
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The amount of force applied on the stress area of a thread. Fine threads have a greater tensile stress area than coarse threads.
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thread
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A raised, helical ridge around the interior or exterior of a cylindrically shaped object. Threads are found on screws, nuts, and bolts.
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thread cutting
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A method of producing screw threads that generally uses a single-point tool to cut a blank or workpiece as it rotates on a lathe.
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thread form
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The shape or profile of a thread. Thread forms include V or square threads.
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thread rolling
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A cold-forming process that uses hard dies to press threads into a solid blank or workpiece.
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thread series
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A thread designation that identifies the coarseness or fineness of threads.
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threaded fastener
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A type of fastener that contains threads. Bolts, screws, and nuts are examples of threaded fasteners.
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thread-rolling die
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A component that shapes metal using extreme pressure into grooved rollers to form threads.
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threads per inch
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The decimal equivalent of the number of threads in an inch.
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tolerance class
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A number and letter combination that indicates the degree of fit and whether it is an internal or external thread.
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Unified coarse
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A thread designation for thicker threads.
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Unified fine
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A thread designation for thinner threads.
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Unified screw thread
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A standard thread form based on inches that was developed by the U.S., Canada, and Great Britain.
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V-shaped thread
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A type of thread form that has symmetrical flank angles with a 60° included angle. The V-shaped thread is the most common thread form for fasteners.
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welding
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A joining process that uses heat, pressure, and/or chemicals to fuse two materials together permanently.
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