Intro to Fastener Threads 110

This class describes fastener threads and their characteristics, as well as explains different thread standards and classifications. Includes an Interactive Lab.

Class Details

Class Name:
Intro to Fastener Threads 110
Number of Lessons:
Additional Language:

Class Outline

  • Objectives
  • What Is a Fastener?
  • What Is a Thread?
  • Thread Characteristics
  • Common Threaded Fasteners
  • Parts of a Thread
  • Measured Parts of a Thread
  • Thread Forms
  • Thread Manufacturing
  • Thread Standards
  • Unified Threads
  • Metric Threads
  • Coarse and Fine Threads
  • Unified Thread Pitch Standards
  • Class of Fit
  • Summary


  • Define fastener.
  • Define thread.
  • Describe common thread characteristics.
  • List common threaded fasteners.
  • Identify the main parts of a thread.
  • Identify the measured parts of a thread.
  • Describe common thread forms.
  • Describe how threads are manufactured.
  • Identify the major thread standards.
  • List common Unified thread specifications.
  • List common Metric thread specifications.
  • Distinguish between coarse and fine threads for fastener applications.
  • List the common thread pitch standards.
  • Distinguish among classes of fit for threads.


  • Job Planning, Benchwork, & Layout I


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