The G-Wizard Calculator Threads page provides handy reference material on threads of various kinds.
Unified/ISO
This page provides information on Unified and ISO Metric threads. To use the page, begin by selecting a Family, Size, and thread Class from the dropdowns on the top left part of the page. You’ll see tapping drill recommendations directly below for those threads (assuming they’re not too big that there won’t be a tap/drill combination). Note that cutting taps require different recommended hole sizes than form taps.
Over on the right is a stylized drawing of the thread with dimensions such as Pitch. You can select either the Internal or External version.
For cutting threads on a lathe, the thread depth section between Family/Size/Class and Tapping Drill is important. It tells you for various thread categories how deeply to plunge the tool to cut the thread. For example, if you are using a sharp-pointed 60 degree “V” tool, use the “Sharp V-Thread Depth.” If you have a UN form tool with the proper radius at the end, use the UN or UNR (for external threads) depths.
Pipe Threads
National Pipe threads are covered by the “Tapered” tab of the Threads page. To select a thread, first choose the Family and then choose the Size from the dropdowns in the top left corner. The correct tap drill and tapping depth will be presented below. Note that this is the tap drill for a non-reamed hole. If you ream with a pipe reamer, a different tap drill is called for. That recommendation will be added to a later version of G-Wizard.
On the right is a stylized drawing of the internal and external threads with dimensions for the various features. Since National Pipe threads are tapered, there are pitch diameters taken against a number of significant locations along the thread per the spec.
Even More Threads: G-Wizard Thread Calculator
The basic threads come with G-Wizard by default. And, for a limited time, you will have access to the additional threads provided by G-Wizard Thread Calculator.
