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Types of Thread Taps: How to Choose the Right One?

January 23, 2025 · About 3 minutes
types of thread taps
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Internal threads are the essential features in numerous mechanical components to fasten them together and build a single item or serve some specific functionality. They facilitate secure and adjustable connections for screws, nuts, etc. But do you know how they are made inside a drilled hole? Well, there are many types of thread taps for this.

This article will discuss 13 different types of thread taps, their sizing, tolerance table, and pro tips at the end for efficient thread tapping.

What’s Thread Taps?

Thread taps are an important manufacturing tool for creating the threads (continuous helical edges) on drilled holes to accept the corresponding bolts or screws. Depending on the types of taps, they come in diverse sizes, geometries, and capabilities. Meanwhile, the tapping can be done manually with tap handles, whereas integrating these tools into CNC drilling machines automates the process.

In manual tapping, a fitting die rotates the tap (size equal to the inside diameter), and then it removes the material from the surface, creating the threads. On the other hand, the tool holder rotates the tap at a fixed RPM using a drilling machine. Wherever method you use, the tapping tools decide the final quality and accuracy.

Standard Tap Markings

A standard tap includes different information written in its body with a marking or engraving process. Moreover, it is a systematic approach that tells the user the capability of any tap. A typical format of marking is shown in the figure below;

Thread tap marking

Nominal Size

The nominal size of a tap refers to the external diameter of the thread it will cut or the major diameter of the corresponding thread faster that will fit after cutting. You can see the information related to this marking on the tool. For example, M6 means the tap will create a thread with a nominal diameter of 6 mm.

Thread Form Symbol

It defines the type and characteristics of threads for tapping, which allows you to choose the right tool according to the desired shape, size, and other specifications. They are denoted by the corresponding thread designation.  For example, unified thread forms(UN) are popular types and it has other related forms like UNC, UNEF, UNJC, and NPTR. Other thread form symbols include ANPT, AWWA, BA, etc.

Tap Material

High-speed steel, carbide, cobalt, and other tough materials are common to make different kinds of taps. Which one to use depends on the workpiece material type, the complexity of desired threads, and precision. The carbide tool can tap stainless steel and titanium, whereas high-speed steel taps struggle for these materials.

MaterialDurabilityThermal ResistanceCompatible Workpieces
HSSMediumUp to 600°CSoft materials like mild steel, aluminum, copper, plastics, etc.
Cobalt (HSS-Co)HighUp to 650°CStainless steel, titanium, cast iron, etc.
CarbideVery HighUp to 1,000°CHardened steel, stainless steel, cast iron, nickel alloys, and titanium.
Titanium Nitride (TiN) CoatedVery HighVariesCarbon steel, alloy steel, aluminum, etc.
Powdered MetalHighModerateTool steels, hardened steels, high-tensile alloys, etc.

Pitch Diameter Limit

The pitch diameter is the diameter of an imaginary cylinder that passes through the thread profile or diameter, excluding the extended flanks of threads. It is crucial as this decides the tightness or looseness of the thread with the counterpart bolt or fastener. Consequently, there is a limit to the maximum allowable pitch diameter based on the function and nature of threads.

Types of Thread Taps

Hand Taps: For Manual Threading

These types of thread taps are used for manual thread cutting of different sizes. Typically, three taps work together in the process: taper, bottoming, and plug tap.

  • Taper Tap: It starts the threading in blind holes to be tapered with a tap chamfered 8-10 threads at the starting.
  • Bottoming Tap: It performs deep bottom threading efficiently with the help of 1-2 chamfered threads at the tip.
  • Plug Tap: It is an all-purpose tap but is mainly used for threading through holes. The  3-5 chamfered threads provide a middle-ground cutting action. The difference between plug tap vs taper is that taper is mostly suitable for starting only.

Pipe Tap: For Tight Sealing

Pipe threading process

Pipe taps are essential for the mechanical fitting and coupling of pipes or tubes. They form both straight and tapered threads on the internal pipe surfaces. In many selling applications like hydraulic systems, oil & gas pipelines, and pressure systems, pipe taps provide tight sealing between the joining components. The threaded fittings with pipe taps also comply with the NPT and NPS classification standards.

Spiral Flute Tap: Removes Chips In Deep Holes

As the name suggested, the spiral flute tap involves helical or spiral flute teeth to cut the deep threads. This tapping tool is known for efficient chip removal in the blind hole threading processes. The spiral flow of flutes in a downward motion facilitates the upward removal of chips at the same time.

Furthermore, you can use the spiral flute tap with various angles, 5, 10, 20, 30, 45°, etc. The lower angles are suitable for hard workpieces, whereas higher angles provide faster cutting speed for ductile materials. 

Gas Tap: Specialized Tap For Gas Fittings

Gas taps contain deep threads in cylindrical and conical pipes.  These specialized types of thread cutting taps can create tight fitting for gas networks and systems. Additionally, gas taps are also useful for hydraulic fitting applications.

The tight fittings in gas valves, nozzles, and mounting parts ensure their efficient function and safety.

Machine Tap: Automatic Taps For Power Machines

A machine tap is a CNC and drill press compatible tool that can perform automatic thread-cutting operations. It is made with tough and durable materials like carbide and HSS with titanium-nitride coating for power tapping tasks. So, you can tap holes (blind and through) on hard hard-to-machine materials like titanium alloys and tool steels.

The computer control of the drilling arm and automation significantly reduces the production time, which makes it efficient for cutting threads in high volumes. However, there is the risk of breaking taps and wear, and optimal tapping parameters are required to avoid this.

Thread-forming Tap: Creates Threads Without Cutting Material

HSS thread forming tap

A  form tap creates the threads by material deformation instead of material removal. Thread-forming taps are pushed or compressed into holes manually or with machines that spin and cause plastic deformation to form thread pitches.

 The thread forming process does not involve the chip formations which can increase the friction and heat-build up. So, oil-based coolants are recommended to avoid this issue. Consequently, you can create tapping holes in aluminum, brass, copper, and other relatively soft metals with this tool.

Master Tap: Precision Reference For Threading Operations

It is also known as a universal tool for tapping that comes in various sizes. The flute numbers may vary, 7, 8, 9, or 10, but all of them can cut clean threads in tough metals and superalloys. 

Furthermore, the master tap serves as a precision of the threaded holes. It verifies the threaded hole whether the tolerances are accurate or not. The helix tip pf enters in holes with tapped threads cleaning the profiles with the following cutting faces to desired dimensional specifications. For example, a thread bolt hole on the cylinder head is verified with a standard master tap to ensure they are fit for assembly.

Combined Drill and Tap

A combined drill and tapping tool

A combined drill tap includes a drilling bit at the endpoint and thread-cutting flutes on the extended shank portion. This tool combines the tapping drills and threading processes in a single operation without the need for tool change. As the tool rotates on the workpiece surface the end section creates a hole removing the chips upward, meanwhile the tapping section cuts threads on the drilled surface continuously.

This combination achieves tighter specifications and saves production time and cost. However, it only works best with materials of medium hardness, such as aluminum, brass, and plastics.

Solid Carbide Tap

Solid carbide tap

It refers to taps made with solid carbide composite, a tough and strong material that consists of extremely fine tungsten carbide and cobalt binder. A highly durable tooling material with excellent wear and abrasion resistance. You can tap threads on abrasive workpieces like plastic composites, aluminum alloys, and brass with the solid carbide tap. Moreover, the flute can have a straight or spiral point shape. 

Extension Tap

Imagine cutting a few threads at the end of a long blind hole; how will a standard tap execute that? Extension taps are used to cut the end threads. These types of taps for threading involve a long straight shank with cutting flutes at the bottom of the body.

Extension taps are useful for complex, long-reach, and blocked holes. Often, the collet is in-built connected with the end of the extended shank to facilitate better clamping.

Spiral Point Tap

It is characterized by spiral flutes that are wrapped in a helical shape around the tap body. The angled cutting edge provides a deep channel for chip ejection in an upward direction. So, you can achieve higher speed and efficiency, including for the blind holes. These taps are available in both manual and power machine operations. The Lower spiral degree ( 5 to 10 °) taps are suitable for hard materials, whereas the higher spiral degree ( 30 to 40 °) is suitable for speed taps and soft workpieces.

Stay Bolt Tap

As the name refers, it creates the threads on thick stay bolts corresponding nuts in pressure vessels like boilers. Its deep and straight flute structure removes the larger volume of chips efficiently. The size of a stay bolt tap varies from 15 to 20”. Meanwhile, it is essential to match the diameter of the threaded hole with the counterpart screw.

Interrupted Thread Tap

The structure of the interrupted thread type involves the removal of the alternative tooth after the cutting edge. This space provides a larger space for chip ejection and can cut deep threads without clogging.  You can use interrupted types of thread taps for heavy chip removal in cylindrical holes, pipes, and tubes.  Subsequently, the lesser cutting faces also reduce the friction and heat generation.

Thread Tap Sizing Table

Designers manufacturers use thread tap sizing charts to choose the right drill bit and tap size. It includes systematic information about drill diameter, tap diameter, depth, thread spacing, etc.

Below is the standard form of a tap sizing table;

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 Table

This table illustrates the matching tolerance codes for taps and internal threads. So, operators and engineers can make wise decisions for the right combination to activate desired precision. The thread tap tolerance table contains all the tolerance systems that comply with ISO2857.

The matching tolerances are critical to ensure the perfect fit of threaded parts during the assembly.

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

How to Choose the Right Thread Tap for Your Project?

The selection of a tap that addresses all specifications of threads requires different considerations. You must match the material compatibility, thread geometrical variables, fit clearance for assembly, etc.

The following are the key considerations for the selection process of the thread tap tool;

Select Based on Material Type

First, consider the workpiece material where you need to tap the hole. Choose a tap made with such material that can machine the work material. There are three tap materials HSS, carbide, and carbide with nitride coating. The HSS is suitable for soft materials like aluminum and thermoplastic, whereas you need carbide taps with nitride coating to cut thread on tough materials like titanium and hardened steel.

Match to Required Thread Pitch

Thread pitch refers to the spacing between the threads. It is one of the most crucial parameters that defines thread characteristics and fitting. So, choosing the type of tap requires considering the desired pitch size and looking for a suitable tap size that can achieve that sizing of the pitch.  For example, if you need the required pitch of 1.5 mm, the tap with an M10 x 1.5 marking matches that requirement. Additionally, you also need to consider the fit for assembly. For this same example, M10 x 1.5, H2, 5G, and 6H codes match the standard fit tolerances.

Determine for Blind or Through Hole

Check-in which type of hole you are going to tap, blind or through hole. Chip evacuation is not an issue in through-hole, whereas blind holes require upward chip removal to avoid clogging and thermal damage. For blind hole threading, you can opt for a spiral point, bottom, spiral flute, etc.

Consider Fluting Needs

The fluting needs typically involve how many flutes you need for better tapping results. Based on the types of thread taps, they might consist of 2, 3, 5, 7, 10, or a higher number of flutes. The tool with fewer flutes is suitable for hard material and blind holes. On the other hand, more flutes increase the speed and are best for the holes that are through.

Additionally, the geometry of flutes also affects the chip removal. The straight flutes direct the material to the bottom. On the other hand, the spiral flutes push the chips forward or upward, depending on the hole type.

Choose for Chip Removal Requirements

Besides fluting needs, consider how long the hole is, the size & thickness of the chips, the removal rate to avoid clogging, and other requirements. For instance, spiral or spiral point flutes are best for long chip removal, whereas straight flutes are ideal for short chips.

Consider Right-Hand or Left-Hand Threads

The right or left hand refers to the thread cutting direction in tapping. So, you need to consider which direction you want to tap the hole, it might depend on the material type, clamping condition, and other factors. The right-hand taps are best for standard rotation needs, whereas the left-hand favor the projects requiring reverse threading.

Pro Tips for Efficient Thread Tapping

The following are some proven tips you can follow for an efficient tapping;

Choose the Correct Drill Size

The drill size directly influences the tapping process; the hole size must be compatible with the tap size you later going to create. So, choose the tapping bit size from the drill size chart that corresponds to the desired tapping specification.

Select the Appropriate Cutting Fluid

The friction between flutes and holes during tapping results in heat-build up, which affects the thread quality and can damage the tool. Cutting fluids is essential to counter this issue, such as oil or lubricant-based coolants for cooling. Moreover, cutting fluids also addresses the clogging and chip build-up problem, facilitating the efficient and clean machining process.

Keep the Tap Straight

Maintaining a straight tap refers to perpendicularity between the workpiece and the tapping bit. Any deflection might cause dimensional inaccuracy and project failure. Ensuring this perpendicularity requires a tapping guide, center punch, and tap-holding pressure to ensure stable alignment.

Apply Optimal Cutting Speed

Cutting speed impacts the quality of chip formation and precision. Inappropriate (lower) speeds can even lead to tap breakage and workpiece damage. Therefore, you need to optimize the cutting speeds by considering the workpiece material type, pitch size, hole type & depth and conducting the test runs.

Reverse Tap Periodically

The best practice to avoid chip accumulation is periodic taper reversing. It includes rotating the tap in the opposite direction after completing a specific number of turns, which helps to form the small chips. For example, rotate the tap counterclockwise periodically if you are using right-hand cutting.

Clean Tap Frequently

Tap cleaning is very essential to maintain its performance and lifespan. Regular cleaning ( after certain production cycles) prevents debris buildup, rust formation, and surface degradation.

Conclusion

CNC machining processes use different types of taps for threading the holes present in diverse materials, from thermoplastics to titanium alloys. Meanwhile, the diverse tap options allow manufacturers to tap the holes with strict requirements.

You need to select a suitable tap that matches your design specifications. The choice of tap depends on the material, hole type, thread size & geometry, and required precision for perfect fitting during assembly. Moreover, the quality of thread taps itself affects the results.

If you are looking for a manufacturer to machine parts with internal threads, RapidDirect can be a viable option. Our CNC machining services can create threads on Milling, Turning, Laser Cut, Drilling, and EDM-machined components. Our engineers analyze the drawing and choose the right types of thread cutting taps to achieve accurate threads efficiently.

We can also coat and harden the threads or components with threading features with the heat treatment processes. For more details about our capabilities, contact us now!

FAQs

1. What type of tap is best for starting threads?

A taper tap is best for the starting threads, which involves 8 to 10 flutes with a gradual taper. This flute geometry distributes the cutting force uniformly and guides the tap smoothly into the hole.

2. What’s the difference between a bottoming tap and a regular tap?

A bottoming tap can cut the thread all the way to the bottom of a deep blind hole, whereas a regular one is unable to do so. It contains a nearly flat tip; only 1–2 threads are tapered.

3. What’s the difference between a plug tap vs. bottoming tap?

The main difference is the number of chamfered threads, bottoming has only one or two at the start and plunge contains many chamfered threads(4, 5, 6, or 7), suitable for through holes.

4. Is it possible to thread holes with a die?

Dies are only used to cut external threads on cylinders, bars, and pipes. They are unable to thread holes. You need to look for different kinds of taps for hole threading.

5. What’s the reason for lubricating a thread tap before use?

Typically, softer material like aluminum and brass tends to wrap with a tap during wrapping. Lubricating helps to prevent this.

6. Can a thread tap fix or rethread an existing hole?

Yes, a thread tap can rethread an existing hole by removing the minor material from the surface. However, it can increase the clearance if the existing threads have any damage.

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    Written By
    Noah Harrison is the Director of Content Marketing at RapidDirect with over a decade of experience in content writing. He specializes in creating custom content for research projects, thesis, and reports, and is skilled in 3D modeling, rendering, and designing innovative products for engineering assignments and advertising.

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