Form tap drill sizes chart full#
Form tap drill sizes chart iso#
Form tap drill sizes chart series#

The UN specification specifies that the common height of a thread should be 5/8 th of this maximum height.ħ5% to 80% thread roughly equals 5/8 th of this maximum height.

Form tap drill sizes chart full#

Thread percentage: (77% thread is what you want to use) A 100% thread is 3/4 qtr, or (6/8 th), of the full 60° triangle which is the maximum allowed height of a full thread, the 'V' shape, including flats. NOTE: The tap drill size of a hole that will be cold form tapped is usually bigger than it cutting tap counterpart. These taps have no 'flutes' and are usually oval shaped or not quite round. Form tap: (Cold forming tap) A tool that makes the helical portion of a threaded hole by forming, or deforming, the material as it moves along a predrilled hole. They should be used in that order when tapping holes that do not break through. Cutting taps usually have sharp 'flutes', somewhat like the spirals of a drill, where the chips can accumulate and be ejected out of the hole NOTE: Cutting taps come in sets of 3 A starter tap, a midway tap, and the bottoming tap. Cutting Tap: A tool that makes the helical portion of a threaded hole by cutting material as it moves along a predrilled hole.

Form tap drill sizes chart series#

NOTE: Most basic sizes have a coarse and a fine series of thread. Pitch: (Distance between each thread, or 'V's.) The distance the a screw or nut will advance every 360° turn. NOTE: If the length of the threaded portion of a screw or threaded hole is shorter or longer than one inch, the size of the 'V' shape is still defined by the number of thread that would fit along a one inch length. TPI: (Threads per inch) The number of thread, or 'V's along a one inch length which in turns, defines the size of the 'V' shape of the helical portion of a thread. NOTE: The size of the hexagon of a bolt or nut has no relevance when defining a thread size. The biggest external diameter of a Screw or the biggest internal diameter of a threaded hole. Outside diameter: This is the biggest diameter of the helical portion of a thread.

Form tap drill sizes chart iso#

NOTE: The American Metric UN thread standard is compatible with the international ISO

Making a thread that follow these specifications will ensure that it will work with threaded holes or shafts made by other manufacturers that follow theseĬommon specs. Metric UN: (American Metric Unified National thread form) A standard that describes the shape of an internal or external thread using Imperial UN: (Imperial Unified National thread form) A standard that describes the shape of an internal or external thread using imperial inch dimensions.

But it’s the machinist who decides which tapping style to use depending on the job at hand.Glossary TDS: (Tap drill size) The size of the hole that must be drilled before a tapping operation. Compare that to cut threads, which because of the tools used, cause grain structure to essentially fracture.Īlso, formed taps have a longer life, as they last about three to 20 times longer than cut taps.Ĭutting taps and forming taps both have benefits and limitations from stronger threads to greater compatibility. But machinists aren’t limited to the materials when they decide to cut taps.Ĭutting taps also have the upperhand regarding horsepower, as this threading method requires less power than forming taps.įormed threads are stronger because the grain flow of materials is compressed at the crest and root of the thread form. When machinists use forming taps, they can only use the process on aluminum, soft steel and nonferrous metals. The two threading methods tap holes differently, but they also have a handful of other differences, starting with the type of thread each method produces.Ĭutting taps are more versatile than forming taps and can be used with more materials.

Additionally, forming taps usually require a larger hole because this style causes a material to thread away and into the threads of the tap. Forming taps involves the displacement of a material (like metal) within a hole. Unlike cutting taps, forming taps create external threads.

This gradual cutting motion allows a tap to smoothly enter a hole. This process then leaves an internal thread that meets the machinist’s desires.Ī machinist achieves that geometric precision by using tools that come with a feature called the chamfer, which cuts a 90-degree angle or edge to make it more symmetrical. Cutting a tap means using tools that remove material from the tapped hole, according to North American Tool. When machinists need to create internal threads, they opt for cutting taps. Cutting taps and forming taps produce threads that are interchangeable and gauge identically, but those are the only similarities between the two tapping styles.