Threads, Bolts, Nuts, Washers

Thread Introduction

  • Thread Terminology - either external threads (male) or internal threads (female)
  • Thread Forms - each thread form is designed to meet a specific requirement
  • Unified Threads - abbreviated as UN and further broken down in coarse (UNC), fine (UNF), and extra fine (UNEF)
  • Metric Threads - abbreviated as M, based on the nominal outside (major) diameter of an external thread and the pitch.
  • Acme Threads - use to transmit power as in jacks for lifting loads
  • Buttress Threads - use to transmit power as in jacks for lifting loads
  • Taper Pipe Threads - V-shaped thread with a taper and designed to produce a seal between the threads of the mating parts
  • Methods of Displaying Threads - simplified, schematic and detailed
  • Designations - general tolerances on prints do not apply to thread features. Must lookup the ASME standard to determine the thread tolerances
  • Unified Threads - example 1/4-20 UNC-2A
    • 1/4 = 0.25“ nominal bolt diameter
    • 20 = Threads Per Inch (TPI)
    • UNC = Unified Coarse
    • 2 = class of fit
    • A = external threads

Screw Thread Designation

  • Screw Thread Designation
    • see Unified Inch Screw Threads (UN and UNR Thread Form) ASME B1.1-2003, p. 61
  • Screw General Symbols
  • Identification of 60-deg Inch Screw Threads
    • see Unified Inch Screw Threads (UN and UNR Thread Form) ASME B1.1-2003, p. 95
  • General Thread Symbols
    • see Unified Inch Screw Threads (UN and UNR Thread Form) ASME B1.1-2003, p. 71
  • Thread Profile from Basic Blueprint Reading
    • Basic Blueprint reading and Sketching by Thomas P. Olivo and C. Thomas Olivo, Publisher Cengage Learning, 2010, p. 100 pdf

Thread Basics

  • Figure 2-0 Fundamental features of a thread from Machine Shop Methods by Lorus J. Milne, p. 98
  • Figure 2-0 Features of a unified thread form from Machine Shop Methods by Lorus J. Milne, p. 103
  • Inventor 2014 saves the Thread.xls spreadsheet in C:\Users\Public\Documents\Autodesk\Inventor 2014\Design Data\XLSen-US folder
  • Autodesk Inventor - coolOrange threadModeler Thread Modeler Tool (need to login with Autodesk ID or email, e.g. NormalOne)
    • Inventor Tools tab > Thread Modeler button, then click a thread to populate the dialog box
    • C:\Users\jensejj\AppData\Roaming\Autodesk\Application\Plugins\Autodesk_ThreadModeler.bundleContents\Thread Templates\SW Template.ipt or ISO Template.ipt
      • Figure 2-0 CoolOrange Thread Modeler in the Tools Ribbon
    • Thread Sketch Template:
    • This plugin was written by Philipe Leefsma, Developer Consultant at Autodesk, working as part of the Autodesk Developer Network program.
    • Support information - email with feedback or requests for enhancements
    • The ThreadModeler tool has been developed to allow Inventor users to generate a realistic modeled equivalent thread based on an existing Inventor thread feature. Users are able to select an existing thread feature in the model, which the ThreadModeler then converts to a realistic 3D modeled thread based on the underlying thread feature properties. Modeled threads are accurately generated saving a lot of time and effort for the user when compared with a manual approach, bringing a higher degree of realism to your models. This plug-in was first published as an ADN Plugin of the Month: The plug-in has been provided with the complete source code needed to build the application, with the intention of encouraging users of Autodesk software to use programming to tailor the products they use to their specific business needs.
    • Figure 2-0 How to Cut Screw Threads in the Lathe, Bulletin No. 36A by South Bend Lathe, p. 13

Standards and Industry


  • Creating a 1/2” Nut (head diameter 3/4“) - Hansen Method
  1. Create a 2D Sketch within Inventor, select the XY origin work plane
  2. Create a 6 sided polygon (hexagon), centered at the origin
  3. assign a dimension of 3/4” across the flats (size of wrench used to install the nut)
    1. Figure 1-0 2D Sketch of 3/4" Nut
  4. draw a 1/2“ circle (size of nut, that is where the nut threads will be applied), assign a 1/2” dimension and then finish the sketch.
  5. extrude the nut 0.375 inches in the negative z-direction
    1. Figure 2-0 3D Sketch of 3/4" Nut
  6. apply a thread (cannot be done in sketch mode). Use an interior thread (class 2B) with size 1/2“ and 32 threads per inch
    1. Figure 3-0 Threads on a 3/4" Nut
  • Creating a 3/4” Hex Nut - ASME/ANSI Method
  1. follow steps in Hansen Method then do the following
  2. On the YZ plane, create the following triangle (interior angle of 30°, adjacent distance of (Gmin - Fmin)/2, and distance from centerline axis of Gmax/2
  3. Revolve around the z-axis, using Full circle cut
    1. <b>F</b> is the width across the flats, also known as the size of wrench to use.
    2. <b>G</b> is the width across the corners
    3. Nut size (interior hole diameter) is the size bolt that the nut is used with, not the size of wrench used to adjust nut. Same applies to washers and bolts, purchase based on the diameter of the bolt, not the head size (see - Measuring Fastener Diameter).
    4. Figure 4-0 Common Diameter for Bolts, Washers and Nuts
    5. Table showing the Bolt diameter (how it is purchased) and the wrench/head used to install it US Bolt Head/Wrench Size
    6. Figure 4-0 Chamfer on a 3/4" Nut
  • Create a 3/8“ Hex Nut - ASME/ANSI Method
  • Figure 4-0 3/8" Hex Nut with corner Chamfers on both sides

Height of UN External Thread

  • Height of UN External Thread = hs = 0.54126588 * Pitch
  • Machinery's Handbook 27th, Table 1. American Standard Unified Inch Screw Thread Form Data, p. 1734
    • Thread Height

Pitch Diameter Tolerance

  • Pitch Diameter Tolerance

AutoCAD Drafting Threads

Thread Depth

Thread Inspection

NOT GO (LO) Thread Ring Gages

  • “Starting threads on NOT GO (LO) thread ring gages are subject to greater wear than the remaining threads. Such wear in combination with the incomplete threads at the end of the product thread permit further entry in the gage. NOT GO (LO) functional diameter is acceptable when the NOT GO (LO) thread ring gage applied to the product external thread does not pass over the thread more than three complete turns. The gage should not be forced. Special requirements such as exceptionally thin or ductile material, small number of threads, etc., may necessitate modification of this practice.” (ASME B1.2-1983 Gages and Gaging for Unified Inch Screw Threads, p. 128)

Thread Cutting Videos

  • Toms Techniques
    • Thread Cutting on the Lathe, Part One - Threading Tool Geometry
    • Thread Cutting on the Lathe, Part Two - Calculating the Flat Width and Helix Angle
    • Thread Cutting on the Lathe, Part Three - Grinding the Tool
    • Thread Cutting on the Lathe, Part Four - Setting up the Lathe and Cutting the Thread
  • Open Source Machine Tools

Procedure Cutting a Thread on the Lathe

Step 7 - Chamfer Workpiece at Beginning of Thread

William Sellers - Standard Screw Threads


  • ASME B1.1-2003 Unified Inch Screw Threads
  • ASME B1.2-1983 Gages and Gaging for Unified Inch Screw Threads
  • ASME B1.30-2002 Screw Threads: Standard Practice for Calculating and Rounding Dimensions
  • Screw Thread Calculations by Edward G. Hoffman
    • The Home Shop Machinist, ISSN 0744-6640, published bimonthly by Village Press, Inc
    • 198311-MachineShopCalculationsScrewThreadCalculationsP1
    • 198401-MachineShopCalculationsScrewThreadCalculationsP2
    • 198403-MachineShopCalculationsScrewThreadCalculationsP3
    • 198405-MachineShopCalculationsScrewThreadCalculationsP4

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