Different Types of Thread Taps-Comprehensive Guide

There are lots of different types of thread taps that can be used for tapping internal threads in metal, but do you know how to choose these different thread tap types for different applications? And what else will help you choose a suitable thread tap for your tapping working? This article will clearly help you answer these questions:

What is a thread tap?

Thread Tap Definition:

A thread tap is a tapping tool for processing internal threads with grooves along the axial direction. Also called screw tap. The thread taps are used for tapping or cutting various medium and small size internal threads in metal.

Most thread taps are made of high-speed steel or carbide and are used to process various metals. The thread tapping tools have a simple structure and are easy to use, and they can be operated manually tap or on a machine tap.resize,m fill,w 1110,h 638# - Different Types of Thread Taps-Comprehensive Guide

For the production of small-sized internal threads, the thread tap is almost the only machining tool.

Tapping metal threads is a relatively tricky machining process because the thread tap is almost buried in the workpiece for cutting. Its processing load per tooth is more significant than other tools. The contact surface of the tap with the workpiece along the thread is huge. When cutting the thread, It must contain and exclude chips. Therefore, it can be said that the tap works under very harsh conditions.

What are the different types of thread taps?

According to a different drive: hand taps and machine taps.

  • Machine taps usually refer to high-speed steel taps with high manufacturing precision. The machine taps are suitable for tapping on machine tools;
  • Hand taps refer to carbon tool steel or alloy tool steel rolling (or incisor) taps, suitable for manual tapping.

According to the processing method: thread cutting taps and forming taps. 

According to the threads to be processed: metric thread taps, metric fine thread taps, and pipe thread taps.

According to its shape, it is divided into straight flute taps, spiral fluted taps, and spiral point taps.

According to standards: DIN taps, ISO taps, JIS taps, and ANSI taps.

According to the material: ordinary HSS taps, cobalt taps, and carbide taps.

In this article, Heygo will explain more about the following thread tap types: straight flute taps, fluted spiral taps, spiral point taps, and forming taps.

1, Straight Flute Taps

Straight flute taps are the most commonly used type of thread tap. The Straight taps are made of high-hardness materials such as high-speed steel and cemented carbide. Straight flute taps can have 2, 4, and 6 teeth in the cutting cone. The cutting speed is slower. The long shank straight flute tap is used for through holes, and the short shank Straight taps are used for blind holes.

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Advantage of straight flute taps:

  • Straight flute taps are easy to tapping metal threads but have slightly lower precision and larger output.
  • Straight flute taps have been widely used in the machining industry because of their convenient processing, low price, and robust versatility.

Disadvantages of straight flute taps :

Strong versatility means weak pertinence. Therefore, straight fluted taps are not suitable for tapping plastic materials with strong ductility (such as stainless steel, titanium alloy, etc.). Significantly when the thread depth of this kind of material exceeds two times the diameter, it is not recommended.

Straight flute taps Application:

  • Straight flute thread taps are widely used for tapping internal threads of ordinary lathes, drilling machines, and tapping machines.
  • The straight flute tap has the best versatility and the most strong rigidity. Therefore, straight flute taps are generally preferred when tapping metal threads with higher hardness (such as threading hardened steel above 40HRC) and powder particles (such as threading cast iron and cast aluminum).
  • Regardless of through-hole or blind hole, metal and non-metal, standard steel, and various non-ferrous metals can be processed.

2, Spiral Flute Taps

Spiral flute taps are mostly used for drilling blind holes in CNC machining centers. Spiral flute taps are divided into left-hand spiral flute taps, and right-hand spiral flute taps are mainly developed to solve deep hole thread tapping. The "deep hole" here refers to a threaded hole with a depth-to-diameter ratio> 2. According to different working conditions, different spiral angles are used. The common ones are 15° and 42° right-handed.

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The advantages of spiral flute taps:

  • Long service life: Compared with ordinary straight fluted taps, the life span of spiral fluted taps can be increased by 30%~50%, and some up to 2 times. This is because the chips are quickly discharged along with the spiral flute tap during the tapping process and will not be blocked in the groove and will not be discharged. There are few chipping and breaking phenomena, which improve the service life.
  • High efficiency and low cost: For tapping metal threads in difficult-to-machine materials, such as tapping blind hole and cutting threads in stainless steel, structural alloy steel, and various non-ferrous metals, with spiral groove taps, only need to use one tap for processing, and does not need to use grouped taps for processing.
  • When tapping internal thread, there is no need to repeatedly advance and retract the tap to remove chips, which improves the tapping efficiency and saves the high-speed steel materials used to manufacture the taps, and reduce the cost.
  • Adequate cooling and lubrication conditions: Because metal chips can be automatically discharged along with the spiral flute, it is not easy to block, the cooling and lubricating needs during cutting are improved, and the heat generation of the cutting part of the tap is reduced. This also enhances the durability of the tap.
  • Smooth cutting, easy to buckle, low roughness
  • Small torque: Due to the smooth chip removal, the chips are not blocked in the narrow chip flute, and the existence of the helix angle increases the actual work
  • Angle, so the torque is small, generally about 30% smaller than the straight flute tap.

Disadvantages of spiral flute taps:

The spiral flute taps are not competent large-size thread tapping work. When tapping large-size threads, especially high-tensile-strength materials, the torque required to use spiral flute taps will be enormous. Such a vast torque can easily cause the tap to collapse or even break. Therefore, the commonly used spiral flute tap specifications are between M3-M36.

Spiral flute taps application:

  • Generally speaking, spiral fluted taps are almost the first choice for blind hole tapping of flexible and ductile materials with long chips (such as cutting threads in stainless steel). The primary consideration here refers to thread tapping of small and medium-size (≤M36).
  • Spiral flute taps are more suitable for processing non-through hole threads (also called blind holes), and the chips are discharged upward during processing. The tap's actual cutting rake angle will increase as the helix angle increases due to the helix angle.
  • Experience tells us: For processing materials with higher hardness, the helix angle should be smaller, generally around 30 degrees, to ensure its rigidity and help extend the tap's life.
  • For processing non-ferrous metals such as copper, aluminum, magnesium, and zinc, which are not very hard materials, the helix angle should be more extensive, about 45 degrees, and the cutting is sharper suitable chip removal.

3, Spiral Point Taps

Spiral point taps are also called tip taps, characterized by opening a wedge-shaped groove on the head of the straight flute tap, changing the cutting cone's shape, and the chips are discharged forward cutting. It is suitable for through-hole thread and deep thread tapping.

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Advantages of spiral point taps:

  • Spiral point machine taps have fast cutting speed, regular size, and clear tooth pattern.
  • Spiral point taps have the advantages of high strength, long life, fast cutting speed, regular size, clear tooth pattern (excellent teeth), etc.
  • Chips are not easily entangled
  • High flexural strength
  • Good cutting performance

Spiral point taps application:

  • The effect of tapping threads in non-ferrous metals, stainless steel, and ferrous metals is perfect, and the spiral point taps should be preferentially used for through-hole threads.
  • When processing the thread, the chips are discharged forward, and the through-hole thread should preferentially use the tip tap.
  • Chips quickly form curled materials

4, Forming Taps

Forming taps are a kind of chipless processing technology that uses metal forming to process internal threads, called screw taps.

Unlike the above three cutting taps, the tapping method of forming taps is to extrude the bottom hole's internal thread shape through the plastic deformation of the material itself. Therefore, the target processing material cannot be too hard.

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Forming taps advantage:

  • The thread extruded by the forming tap has a smooth surface, good precision, wear resistance, breakage resistance, and high strength. It is widely used in the electronics and plastic industries.
  • No chips are generated, so 90% of processing problems can be eliminated.
  • The threaded holes processed by the extrusion forming process have high tensile and shear strength, and the roughness of the processed surface is also good.

Disadvantages of Forming taps:

Because it is extrusion molding, there are fine grooves on the top of the processed internal thread, so it is not suitable for work types that require high tightness.

Forming taps application:

  • Suitable for processing materials with lower strength such as tapping threads in aluminum alloy,
  • Right ductility materials (aluminum alloy, copper parts, low, medium carbon steel)
  • Blind hole and through-hole tapping

Thread Tap materials

Commonly used materials for thread taps are various high-speed steels(HSS) and cemented carbides. Its hardness varies according to different materials—ordinary high-speed steel: 62~64HRC, cobalt-containing high-speed steel: 67~68HRC, and cemented carbide: 69~79HRC.

Like carbide tools gradually replacing high-speed steel tools in CNC turning, carbide taps have also begun to be used more for threaded hole processing.

Compared with HSS taps, carbide taps have higher hardness and greater brittleness. Use carbide taps to tap There is a problem with chip disposal. Nevertheless, cemented carbide taps are very useful in tapping threads in cast iron, aluminum alloy materials, and the main form of damage to the taps is mechanical wear.

As the automobile industry processes, many cast iron and aluminum alloy parts, carbide taps are used to obtain long tool life. When processing workpieces of these materials, carbide taps have a longer life than high-speed steel taps, in the automotive industry, the reduction of the tool change time of the wire push is an essential factor, and the long life of the carbide wire push will minimize the tool change time.

1, HSS Taps

High-speed steel (HSS) is a more popular tap making material. Although high-speed steel taps have the disadvantages of high temperature and vibration, they can still maintain their integrity during tapping. There are various types of high-speed steel with different hardnesses.

According to different materials, ordinary high-speed steel: 62~64HRC, cobalt-containing high-speed steel: 67~68HRC, but the main "components" include high-carbon tool steel, tungsten, chromium, vanadium, and iron.

HSS tap is best suited to penetrate relatively soft metals, such as alloy steel, cast iron, copper, magnesium

For tapping internal threads in cast iron or other ductile materials, nitride/oxide treatment HSS can be used, which helps prevent tap wear. Other coatings, such as titanium nitride (or aluminum titanium nitride), can also improve the tap's durability.

2, Carbide Taps

Cemented carbide is much denser than high-speed steel and has high friction and heat resistance.

Although resistant to abrasives, solid carbide, like other tap materials, tends to become brittle and cannot withstand vibration. Therefore, solid carbide taps should only be used with modern high-speed cutting equipment with minimal vibration during operation.

Solid carbide taps can process many different materials, such as tapping threads in alloy steel, aluminum, brass, carbon steel, cast iron, copper, Hardened steel, Inconel, Nickel (and other cemented carbide), Sintered material, stainless steel, and titanium.

3, Carbide taps vs. HSS taps

  • Solid carbide tap is more expensive than high-speed steel tap,
  • Cemented carbide taps have super durability.
  • The sharp cutting edge of carbide taps is longer than HSS taps.
  • Using solid carbide taps means you will need fewer taps and spend less time to replace thread taps.
  • Withstand much higher temperatures than HSS.
  • It runs at a higher cutting speed than HSS.
  • Produces cleaner and smoother edges than HSS.

Thread Tap size 

The thread tap size specifications include metric taps and inch taps. For example, metric taps M8*1.2, where M is the triangular thread code, 8 represents the tap's diameter, and 1.2 means the tap's pitch in mm. For example, for the inch tap 5/16-18, the tap's diameter is 5/16 inches, and the 18 behind it means there are 18 threads in 1 inch.

You can find more thread tap size chart:

Tap sizeBasic major
dia (mm)
Basic major dia
(inch)
mm per threadDrill size
(mm)
Drill size
(inch)
M1.6 x 0.351,6mm.0630.351,25mm#55
M2 x 0.42mm.0787.41,6mm#52
M2.5 x 0.452,5mm.0984.452,05mm#46
M3 x 0.53mm.1181.52,5mm#39
M3.5 x 0.63,5mm.1378.62,9mm#32
M4 x 0.74mm.1575.73,3mm#30
M5 x 0.85mm.1969.84,2mm#19
M6 x 16mm.236215mm#8
M8 x 1.258mm.31501.256,8mmH
M8 x 18mm.315017mmJ
M10 x 1.510mm.39371.58,5mmR
M10 x 1.2510mm.39371.258,8mm11/32
M12 x 1.7512mm.47241.7510,2mm13/32
M12 x 1.2512mm.47241.2510,8mm27/64
M14 x 214mm.5512212mm15/32
M14 x 1.514mm.55121.512,5mm1/2
M16 x 216mm.6299214mm35/64
M16 x 1.516mm.62991.514,5mm37/64
M18 x 2.518mm.70872.515,5mm39/64
M18 x 1.518mm.70871.516,5mm21/32
M20 x 2.520mm.78742.517,5mm11/16
M20 x 1.520mm.78741.518,5mm47/64
M22 x 2.522mm.86612.519,5mm49/64
M22 x 1.522mm.86611.520,5mm13/16
M24 x 324mm.9449321mm53/64
M24 x 224mm.9449222mm7/8
M27 x 327mm1.0630324mm15/16
M27 x 227mm1.0630225mm1

Thread Tap Tolerance Chart

The machine taps are marked with the code of the tolerance zone of the pitch diameter: H1, H2, and H3 respectively indicate the different positions of the tolerance zone, but the tolerance values are equal. The tolerance zone code of hand taps is H4, the tolerance value, pitch, and angle error are larger than machine taps, and the material, heat treatment, and production process are not as good as machine taps. H4 may not be marked as required. The internal thread tolerance zone grades that can be processed by the tap pitch tolerance zone are as follows:

The tap tolerance zone code applies to the internal thread tolerance zone grade:

Tolerance code of TapTolerance code of the internal thread
 H14H, 5H
 H2 5G, 6H
H36G, 7H, 7G
 H46H,7H

Tap tolerance chart

Thread Tap Coatings 

Most of the thread tap manufacturers provide coated taps, which have greatly improved the service life and cut uncoated taps. The taps of unequal diameter design have reasonable cutting load distribution, high processing quality, but high manufacturing cost.

The tap's geometry mentioned above, coupled with a unique coating surface (like TiN, TiCN, CrN, or TiAlN), can significantly increase the tap's life. These heat-resistant, smooth coatings reduce cutting forces and allow tapping at higher cutting speeds. The development of newer high-performance taps has dramatically promoted the increase in machine tool spindles' speed and power.

1, TiCN (Titanium Carbon Nitride)-blue-gray, PVD coating process, multilayer coating with a layered structure. TiCN-coated thread taps are generally used for tapping difficult-to-process materials, such as tapping threads in quenched and tempered steel, wear-resistant steel, etc.

2, TiAlN (Titanium Aluminum Nitride)-The appearance is purple and black. It also uses PVD technology. TiAlN coated taps are mainly used to tapping metal threads in castings, such as tapping threads in cast iron and cast aluminum wear-resistant materials and high temperature and high-speed cutting general cooling performance is not good. This coating is the first choice;

3, TiN (Titanium Nitride)-golden appearance, using PVD coating process, easy to produce, low cost, wide application range, generally can increase the tap's life by about 300%. TiN Thread taps also provide additional resistance to heat damage and reduces friction in the tap head, which offers high lubricity and increases chip flow in softer materials.

4, Vap (Vaporized)-high-temperature oxidation treatment, that is, the tap is placed in 530℃ high-temperature water vapor to generate black Fe3O4 on the surface of the tap. The primary function is to absorb cutting fluid to increase lubrication performance and inhibit cutting. The generation and adhesion of nodules have a wide range of applications, especially in the tapping of medium and low-strength steels. The effect is particularly significant;

5, CH (Amorphous Carbon)-Amorphous carbon similar to diamond. The appearance is dark gray. Using the PVD process, the coating thickness is 1-2μm, and the hardness is about 2500HV. Mainly used for tapping of non-ferrous metals and aluminum and its alloy materials.

How to maintain thread taps well?

1. When tapping, the end hole should be chamfered; the tap should be coaxial with the workpiece's hole; axial pressure should be applied at the beginning of tapping to make the tap cut in. After a few turns, no axial force is needed.

2. After the calibrated part of the tap enters the screw hole. It will return 1/4 or 1/2 turn every half turn to one turn so that the chips will be broken and then tap down; when tapping the through-hole, it must be withdrawn frequently Tap for chip removal.

3. When tapping on steel workpieces, add cutting fluid. When tapping on cast iron workpieces, add a little kerosene; after using the first tap, the tap must be screwed into the screw hole when using the second or third tap.

4. When threading, the end of the workpiece should be chamfered, and the end face of the threading should be perpendicular to the axis of the workpiece; the axial pressure should be applied at the beginning of the threading, and the rotating force should be correspondingly larger; when the threading is cutting the thread on the workpiece, Don't put more pressure.

5. To break the chips and discharge them when threading, the teeth should be turned frequently.

6. The workpiece should be firmly fixed on the clamps and fixtures; when the tap is broken, do not touch the broken place with your hands, use a clamp or punch to remove it, and wear protective goggles when the wire is broken.