Taps and Dies are tools commonly used in metalworking for the cutting of threads in metal parts.

Tap

The Tap is used to cut a female thread on the inside surface of a predrilled hole.
The three taps in the adjacent image are of different sizes and types.

• The top tap has the thread going all the way to the end of the tap and is called a bottoming tap - it will tap to the bottom of the hole.
• The middle tap is an intermediate tap where the thread tapers off before the bottom
• The lower tap is a taper tap where the thread has an even more pronounced taper towards the end of the tap. This taper allows the tap to ease into the freshly drilled hole in a gradual cutting action, relieving the cutting pressure on the first few teeth of the tap.

To use, a hole is made (usually drilled) that is the minor diameter for that sized tap. This is the equivalent of the blank size (major diameter), less thread depth.
The order of usage when hand tapping is to use the taper tap first, the intermediate next (if the material is hard and it is felt that the tap is still working too hard), and finally the bottoming tap is used to get the full form of the thread for the full depth of the shank or hole.

For the proper use of this tool see the tap wrench article.

Die

The Die cuts a male thread on a preformed cylindrical rod. The dies shown are

• top left - and older split die, with top adjusting screw
• bottom left - a one piece die with top adjusting screw
• center - a one piece die with side adjusting screw (barely visible on the full image)
• top and bottom right - two dies without adjusting screws.

To use, a cylindrical blank, which is usually slightly undersize the required diameter, is machined with a taper (chamfer) at the threaded end. This chamfer allows the die to ease onto the blank before it cuts a suffecient thread to pull itself along.
The adjusting screws allow the die to be compressed or expanded to accomodate slight variations in size, due to material, manufacture, or die sharpness. The two right most die images shown in the image have no adjusting screws, however the die holder can be used to exert pressure and close the cutting size down if required.

Each tool is used independently, but are usually sold in paired sets of both types, one die and three taps. Some sets however may provide a lesser number of taps. The common or garden variety (shown above) are designed for purely manual operation, but different types such as helical or spiral may be used in production tools such as CNC machine tools.

Rolled Threads

Not all threads are made by a cutting action. In large production runs or where great strength is required, the threads may be rolled, both for the male and female portions.

In the case of the tap there are no cutting edges but instead the tap is lobed. The tap is forced into the hole and the material is deformed by the lobes into the required thread form.
The male portion (bolt) is fed between rollers that have the full thread form ground into their outer diameter. The action of feeding the rollers into the work piece deforms the material into the required shape. Rolled threads have the advantage of increased strength (the material flows into shape, similar to forging) along with reduced material cost as the bar or rod used is actually smaller than the finished size due to the material sqeezing into shape.

Other uses

An ordinary Tap or Die can also be used for repairing threads in stripped holes or bolts. Die Nuts are dies made for cleaning up old threads, they have no split for resizing and are made from hexagonal bar so that a wrench or shifter spanner can be used to apply them (rather than the purpose built die wrench)