Thread Calculator [ Comprehensive Awesome Software ]

3 months by cncdivi

Thread Calculator [ Comprehensive Awesome Software ]

Have you had a chance to try our new Thread Calculator?  G-Wizard Thread Calculator is a premium add-on module for G-Wizard Calculator.  There’s a special limited-time offer that gets you Thread Calculator for half price.

This screw thread software will still work for common UN and ISO internal threads and external threads even if you don’t have the premium module.

thread calculator

What is a Thread Calculator?

Screw Threads are complex beasts.  They’re based on standards that run to hundreds of pages.  We depend on screw threads to be interchangeable if we follow the proper standard correctly.  The goal of a Thread Calculator is to give you comprehensive capabilities to deal with screw threads:

  • Determine Thread Dimensions such as Major Diameter, Minor Diameter, Pitch Diameter, Thread Pitch, and dozens of other variables that specify a screw thread.
  • Present values for both internal threads and external threads.
  • How to check those dimensions, for example use the “Measure Over Wires” technique or what the dimensions should be if you want to make Go/No Go Gages.
  • Tell  you what the tolerances are to keep your screw threads within spec for their Tolerance Class.
  • Calculate all of this for standard and non-standard screw thread sizes.
  • Tell you what tap drills to use for tapping internal threads.
  • Print detailed reports to be used for inspection, quality control, and documentation.
  • Handle the largest possible variety of screw thread types.

G-Wizard Thread Calculator can do all this and more.

The alternative is scouring the net, finding limited tools that only perform one task such as a thread minor diameter calculator.  Or worse, finding dozens of UN thread calculators, but not being able to find help for your important but obscure screw thread at all.

Typical software that’s available today ranges from free for relatively limited calculators to over $1000 for the most sophisticated that includes support for proprietary oilfield tapered threads.

Our G-Wizard Calculator has included a Free Thread Calculator since the beginning.  We’ll keep offering that, but we’re also adding an Advanced Thread Calculator with features and functions that rival the high-end packages at a much more reasonable price.

If you’re going to be programming a CNC for threading, you want high quality thread software at your disposal.

Free G-Wizard Thread Calculator

We were one of the first machinist’s calculators to include screw threads, and our Free Thread Calculator remains one of the most feature rich.  Here is G-Wizard’s Free Thread Calculator:

free thread calculator

As you can see, it’s a pretty nice calculator.  One of my favorite features is the Tap Drill Size chart, which helps you avoid broken taps by selecting the best drill for your application.  Even the free thread calculator has a number of excellent features:

  • Covers both external threads and internal threads for UN and ISO thread standards
  • Covers tapered external threads and internal threads (pipe threads) for NPT.
  • Key thread dimensions presented in graphical form such as pitch diameter, major diameter, minor diameter, threads per inch (or mm), thread pitch, and more.
  • Choose the tolerance classes to determine thread tolerance.

If you just need a basic UN Thread Calculator or ISO Thread Calculator for metric users, it’s hard to beat this free tool.  But, for more exotic screw thread families and for more features and screw thread information, you’ll want our Advanced G-Wizard Thread Calculator.

A Quick Tour of Advanced G-Wizard Thread Calculator

Using G-Wizard Thread Calculator is straightforward.  Follow these steps:

Select the GW Threads tab in G-Wizard Calculator

internal thread calculator

If there is no GW Threads tab, it means you’re not registered to use GW Thread Calculator.  Go to the product page and register for a free trial or purchase.

Select Straight or Tapered (Pipe) Threads

GW Thread Calculator divides screw threads into Straight and Tapered (Pipe threads are often tapered) groups.  Select the tab at top for the one you want.

thread calculator

Select a Screw Thread Family and Preferred Thread Size

Screw Threads belong to families that determine the general shape and geometry of the screw threads.  A Family also has a list of Preferred Thread Sizes that are standard for that Family.  You select both using the dropdowns at the top left of the GW Thread Calculator:

thread calculator

Custom Thread Calculator

Not all families allows custom thread sizes, but many do.  You’ll need to enter a Nominal Size (also known as the Basic Major Diameter) and either TPI (Threads Per Inch) or Pitch (many metric Families use pitch) for your custom thread size.  Given your desired Tolerance Class, GW Thread Calculator will then calculate all the dimensions for the screw thread.

custom thread calculator

Tolerance Classes

Not all thread families have tolerance classes, but when they do, you’ll set them here from the “Class” dropdown.  The tolerance classes tell what the thread tolerance should be on the thread’s dimensions.  Tighter tolerance classes allow less variation from the ideal dimensions while looser tolerance classes allow greater variation (greater thread tolerance).

Thread Starts

Change the number of starts from the default of “1” to create a multi-start thread.

Tapping Drills

Determine the optimal size for your tapping drill based on whether you have a cutting or forming (thread rolling) tap and on what percentage threads you want to create.  Be sure to check out our in-depth article to understand the effect of thread percentages on tap life.

Graphics View vs Report View

Graphics View gives you a quick visual summary of the thread.  Report View has a lot more information and is intended when you want to print a report with as much information as possible about a particular screw thread.

Internal or External Thread

There are views for Internal Threads and External Thread.

CADCAM Thread Wizard

Click this button to load the currently selected thread into CADCAM Wizards.

Measurement Over Wires: Thread Wire Calculator

G-Wizard Thread Calculator includes a Measurement Over Wires Calculator for External Thread measurement of pitch diameter:

external thread calculator

At the top of the MOW Calculator are the Min, Max, and Recommended Best Size to use for measuring wires.  Enter your actual wire size, and the MOW Min and Max for the thread to be in spec are given.  Enter the Size Over Wires you measure and the pitch diameter of the thread will be given.

If you verify the Pitch Diameter using the 3 wire method, you can use G-Wizard to find the correct thread, and from that you will then know the major diameter, minor diameter, and all the rest of the data.  Likewise, if you verify the pitch diameter, flats, and the thread angle, then the other measurements should be correct.

The feature list for G-Wizard Thread Calculator is not frozen yet (see below to give us your input), but here are the major new things that are there:

More Thread Types

It goes without saying GW Thread Calculator will support a lot more thread types than our free version.  Be sure to tell us in the survey below which screw threads are important to you so they’ll be properly prioritized.  Just as we do with all our products, we’ll keep adding more thread types over time with new releases.

Thread Dimension Chart / Report

thread dimensions chart

It’s often important to print reports that contain all the details of a screw thread.  Whether you want a graphical view of the most important dimensions, a quick reference chart of all the details, or a printed report, GWTC has you covered.

Pluggable Standards-Based Engine Architecture

The biggest change from our old Free Thread Calculator is the completely new Pluggable Standards-Based Thread Engines.  Our original Thread Software was built on a database approach.  All the key values were there so very little calculation was needed.  The new G-Wizard Thread Calculator is based on a calculated approach.  It uses the same formulas described in the screw thread standards, such as ASME B1.1-2003 for UN threads.

This accomplishes several things.  One, it makes it possible to calculate screw threads based on arbitrary combinations of Nominal Size and Threads Per Inch.  Second, it makes it easier for us to add large numbers of new screw threads over time, including much more exotic screw threads.

Manual Lathe Guides

Manual Lathe Guides give you step-by-step instructions for how to cut whatever screw thread you’ve selected.  Here’s what they look like:

One thing that’s really cool about them is they tell exactly how many passes need to be made and the depth of cut for each pass.

Screw Thread Families Supported by G-Wizard Thread Calculator

Screw Thread Family / Series Designation


Thread Sizes

Free Screw Thread Families included with G-Wizard

 Unified National: UN, UNC, UNF, UNEF, UNS  ANSI/ASME B1.1-2003  371GW Thread Calculator allows Custom diameter and TPI
 ISO Metric M, Coarse and Fine  ASME B1.13-2005


GW Thread Calculator allows Custom diameter and TPI

Premium Screw Thread Families added by G-Wizard Thread Calculator

 UNM – Miniature Thread Sizes for Watchmaking and similar applications  ASME B1.10  14
 UN STI – Screw Thread inserts such as Helicoil.  UNC and UNF sizes.  ASME B18.29.1-2010  43
 ISO STI – Screw Thread inserts such as Helicoil.  Coarse and Fine thread sizes.  ASME B1.13M-2005  44
 Pg (Panzergewinde) Conduit Threads  DIN 40430  10
 UNJ – Aerospace Thread.  UNJC, UNJF, and UNJEF Sizes  SAE AS8879-D  82
Plus Custom diameter and TPI combinations
Metric MJ – Aerospace Thread.  B1.21M-1997 157
Plus Custom diameter and Pitch combinations
British Standard Whitworth (BSW) British Standard Whitworth (BSW) 19
Plus Custom diameter and TPI combinations
British Standard Whitworth Fine (BSF) British Standard Whitworth (BSW) 16
Plus Custom diameter and TPI combinations
 British Association (BA) BS 93:2008  17


Data Available for Each Screw Thread (including Internal Threads and External Threads) and Definition of Each

Family (also called “Series Designation”)

A thread family broadly determines the thread’s geometry.

Series Designation

Many thread families have multiple series designations.  For example, Unified National includes UN, UNC, UNF, UNEF, UNS and more.


Thread Size specifies a particular thread within a family and series.  Size is typically expressed at least as a size (usually nominal size), and also very commonly as a size and thread designation (such as TPI).

Nominal Size

Thread Sizes are typically given by the nominal size which is slightly larger than the exact measurement.


TPI refers to Threads per Inch.


The name of the standard that determines the thread.  For example ASME B1.1-2003.

Tolerance Class

Thread specification tolerances are determined by the tolerance class.  A tolerance class is in two parts: the tolerance grade and tolerance position.

Series Designation

The full designation of a thread as called out should include the family, size, and tolerance class of the thread.  For example, “1/4-28 UNF-2A” is family UNF, size 1/4-28, and tolerance class 2A.

Thread Angle

Thread angle is the wall angle of the thread.  UN threads have a thread angle of 60 degrees, for example.

Thread Starts

A thread with one start can start at 1 position on the circle of rotation.  2 starts means there are 2 positions on the circle, and so on.


Refer to the diagram to see how thread pitch is measured:


Lead is the linear travel the nut makes per one screw revolution.  Lead is basically Pitch * Thread Starts.

Lead Angle

The lead angle is the helix angle of the thread based on the lead distance.  Multi-start threads have a larger lead angle.

Length of Engagement

Length of thread engagement is measured by the length of interaction between the fastener and nut.

Length of Engagement (Threads)

This is the Length of Engagement measured in threads rather than inches or mm.

Min Major Diameter

Refer to the diagram to see how major diameter is measured:

The major diameter is the largest diameter of an external thread or internal thread.

Major Diameter must be within the range of min major diameter to max major diameter.

Max Major Diameter

Maximum major diameter for this screw thread and tolerance class.

Mean Major Diameter

Mean major diameter for this screw thread and tolerance class.

Min Minor Diameter

Refer to the diagram to see how minor diameter is measured:

The minor diameter is the smallest diameter of an external thread or internal thread.

Minor Diameter must be within the range of min minor diameter to max minor diameter.

Max Minor Diameter

Maximum minor diameter for this screw thread and tolerance class.

Mean Minor Diameter

Mean minor diameter for this screw thread and tolerance class.

Min Pitch Diameter

Refer to the diagram to see how pitch diameter is measured:

The pitch diameter falls between the major diameter and minor diameter of an external thread or internal thread.

Pitch Diameter must be within the range of min pitch diameter to max pitch diameter.

Max Pitch Diameter

The Maximum Pitch Diameter for this thread and tolerance class.

Mean Pitch Diameter

The Mean Pitch Diameter for this thread and tolerance class.

Sharp V-Height

Refer to the diagram to see how Sharp V-Height is measured:

Height if there were no flats on the thread.

Flats Height

Refer to the diagram to see how Flats Height is measured:


Width of the Flat.  See diagram above for a visual.


Allowance is the intentional clearance created between mating threads when the nut and bolt are manufactured.  The allowance ensures the threads turn freely without binding.

The Allowance is specified as part of the external threads, not the internal threads.

Major Diameter Tolerance

Difference between min and max major diameter.

Pitch Diameter Tolerance

Difference between min and max pitch diameter.

Minor Diameter Tolerance

Difference between min and max minor diameter.

Where Do I Get It?

To get G-Wizard Thread Calculator, all you need is a working copy of G-Wizard Calculator.  Once you’ve downloaded the latest GW Calculator, click the “GW Threads” tab to access GW Thread Calculator.

G-Wizard Thread Calculator, a new software product for CNCCookbook, is available for download here:

[ Download G-Wizard with G-Wizard Thread Calculator ]

There’s just one proviso–you must have an active G-Wizard Calculator Trial or Subscription, because G-Wizard Thread Calculator is an add-on module for G-Wizard Calculator.  

What Will it Cost?

G-Wizard Thread Calculator will be a one-time purchase (no subscription needed) that acts as an upgrade for your G-Wizard Calculator.  You make the purchase and you’re done.  Like all G-Wizard Software, all updates and support are yours for life at no additional charge.  As you’d expect, existing G-WIzard Calculator customers will get a sweetheart deal to add GW Thread Calculator.  Expect GW Thread Calculator to be one of the most cost-effective premium solutions in the market.

Do I Need a Thread Calculator?

If you make parts that use unusual thread families or custom sizes, you need it.

If you need all the information you can get about threads for inspection or quality control, you need it.  Thread tolerance is a complex subject, and the detailed information in G-Wizard Thread Calculator can help with that.

If you don’t want to dig through the Internet, Machinery’s Handbook, or expensive thread standards documents, you need it.

Thread Calculator FAQ

You can download G-WIzard for a free 30-day trial.  At the end of the 30 days, assuming you haven't purchased, you still have access to the UN and ISO threads in the Thread Calculator.

G-Wizard Thread Calculator incorporates a full NPT Thread Calculator.

The major diameter is the largest diameter of an external or internal thread.  The minor diameter is the smallest diameter of an external or internal thread.  The pitch diameter is the diameter where the thickness of the screw thread and the space between two threads (i.e. the thread pitch) are equal.  Pitch diameter is sometimes approximated by taking the average of the major diameter and the minor diameter, but this is not a very accurate approximation.

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Recently updated on April 12th, 2024 at 02:55 pm