Different Types of Taps and Their Uses in Machining

Threads are an essential part of nearly every machined component - from automotive engines to aerospace assemblies and precision moulds. When it comes to creating accurate internal threads, taps are the most crucial tools. In CNC machining and metalworking, choosing the right tap type can significantly affect thread quality, tool life, and production efficiency.

There are many types of taps available, each designed for specific materials, hole types, and machining conditions. From spiral flute taps that efficiently remove chips from blind holes to form taps that shape threads without cutting, understanding how each tap works allows machinists to achieve optimal results in threading operations.

In this comprehensive guide, we'll explore the main types of taps, their materials, coatings, and applications, along with expert tips on how to select the best tap for your CNC machine. Let's dive deeper into the world of threading tools and discover how the right tap can enhance your machining performance.

What Is a Tap in Machining?

A tap is a precision cutting tool used to create internal threads inside a pre-drilled hole - a process known as tapping. In machining and manufacturing, taps are indispensable tools for producing threaded holes that can accommodate bolts, screws, or other threaded fasteners. These threads ensure accurate alignment, secure fastening, and strong mechanical connections between components.

A typical tap features flutes, cutting edges, and a shank. The flutes act as channels that allow chips to escape during cutting, while the chamfer at the tip helps guide the tap into the hole and gradually form the thread. Depending on the geometry, taps can either cut material (cutting taps) or form threads by displacing material (forming or roll taps) without generating chips.

In CNC machining, tapping can be performed manually or by machine. Modern CNC tapping operations use rigid tapping technology - synchronising the spindle rotation with feed rate - to achieve precise thread pitch and depth control. Compared to thread milling, tapping offers higher speed and efficiency for smaller holes, making it the preferred method for mass production and precision threading applications.

Main Types of Taps and Their Applications

There are several types of taps used in machining, each designed for specific hole types, materials, and cutting conditions. Choosing the right tap directly affects thread quality, tool life, and machining efficiency. Below, we'll explore the most common tap types and their ideal applications.

1. Hand Taps

Best for: Manual operations and general-purpose threading

Hand taps are the traditional, multi-piece sets used for manual or low-speed tapping. They typically come in three styles - taper tap, plug tap, and bottoming tap - each with a different chamfer length for varying thread depths.

Taper tap: Easy to start threading; used for starting holes

Plug tap: Intermediate type for general threading

Bottoming tap: Used to finish threads to the bottom of a blind hole

Hand taps are ideal for repair work, low-production runs, and soft materials like aluminium or brass.

2. Machine Taps

Best for: CNC machining and automated tapping processes

Machine taps are designed for power-driven machines and CNC systems. They feature precise geometry and higher toughness, enabling stable performance at consistent speeds. Machine taps are available in various flute designs to match hole types and material conditions.

3. Straight Flute Taps

Best for: Brittle materials (cast iron, bronze) and short-chipping materials

These taps have straight grooves along the body, which do not control chip direction. They are mainly used for through-holes or when chip evacuation is not critical. Their simple design makes them strong and cost-effective for tough materials.

4. Spiral Point Taps (Gun Taps)

Best for: Through holes in ductile materials

Spiral point taps, also called gun taps, feature a cutting edge that pushes chips forward - out of the hole. This makes them ideal for through-hole applications in materials like steel or stainless steel. Their design minimises clogging and allows for faster machining speeds.

5. Spiral Flute Taps

Best for: Blind holes and soft materials

Spiral flute taps have helical grooves that lift chips backwards and out of the hole. They are perfect for blind holes where chip removal must be directed away from the bottom. The spiral design also helps reduce cutting force and prevents chip packing.

6. Interrupted Thread Taps

Best for: Hard materials or when torque reduction is needed

Interrupted thread taps have sections of missing threads along the cutting edge, which reduces friction and cutting pressure. This design is especially useful in tough or gummy materials and extends tool life by improving chip control.

7. Forming Taps (Roll Taps)

Best for: Ductile materials (aluminium, copper, soft steels)

Unlike cutting taps, form taps don't remove material; instead, they displace it to form threads. This results in stronger threads with smoother finishes and no chip formation - ideal for high-speed CNC tapping. They also reduce tool wear and require less lubrication.

Main Types of Taps and Their Applications

Taps come in various designs to suit different machining needs, materials, and hole types. Selecting the right tap not only improves thread quality but also extends tool life and ensures smooth operation. Below are the most common types of taps and their practical applications.

1. Hand Tap (Straight Flute Tap)

The hand tap is the most traditional type, featuring straight flutes along its body. It is generally used for manual or general-purpose operations and often comes in three forms: taper, plug, and bottoming taps. This type cuts material by shearing and is ideal for through holes or shallow blind holes in softer materials such as carbon steel and cast iron. Though slower than CNC machine taps, hand taps remain widely used for low-volume or maintenance work.

2. Spiral Point Tap (Gun Tap)

Spiral point taps have straight flutes with a cutting edge designed to push chips forward, out of the hole. This design allows for faster cutting speeds and cleaner threads. They are particularly effective for through-holes, where chips can easily exit. Spiral point taps are commonly used in CNC machining and high-speed production environments, especially for materials like alloy steel and cast iron.

3. Spiral Flute Tap

The spiral flute tap features helical flutes that lift chips upward and out of the hole. This prevents chip clogging and reduces the risk of tool breakage - a common issue in blind hole tapping. These taps are suitable for blind holes and are often used for softer, more ductile materials such as aluminium, copper, and stainless steel. They provide excellent surface finish and thread accuracy.

4. Form Tap (Roll Tap)

Unlike cutting taps, form taps do not remove material. Instead, they plastically deform the workpiece to create threads, which means no chips are produced. This method results in stronger, smoother threads and longer tool life. Form taps are ideal for ductile materials like aluminium, brass, and mild steel, but not suitable for brittle materials such as cast iron.

5. Pipe Tap (NPT, BSPT)

Pipe taps are specially designed to create tapered threads that provide a tight seal for fluid or gas connections. They are widely used in plumbing, hydraulic, and pneumatic systems where leak-free joints are required.

6. Machine Tap (CNC Tap)

Machine taps are specifically engineered for CNC applications. They have stronger shanks, precise geometries, and advanced surface coatings to handle high-speed, high-accuracy tapping operations. With rigid or synchronous tapping cycles, these taps ensure consistent thread quality in mass production environments.

Each of these tap types serves a unique purpose. Understanding their strengths and suitable applications helps machinists achieve higher efficiency, avoid tool damage, and produce precise, durable threads in all types of materials.

Tap Materials and Coatings That Enhance Performance

The material and coating of a tap play a crucial role in determining its performance, durability, and suitability for specific machining conditions. Choosing the right combination can significantly improve cutting speed, extend tool life, and ensure consistent thread quality - especially in high-volume CNC production.

1. High-Speed Steel (HSS)

High-speed steel is the most widely used material for taps due to its excellent balance between toughness, wear resistance, and cost. HSS taps can handle a variety of materials, including mild steel, cast iron, and aluminium. They are suitable for both manual and machine operations, making them the go-to option for general-purpose threading.

2. Cobalt High-Speed Steel (HSS-E)

Cobalt-alloyed HSS contains about 5–8% cobalt, which enhances heat resistance and hardness. This allows the tap to maintain sharpness and dimensional stability under high cutting temperatures. HSS-E taps are ideal for harder materials such as stainless steel, titanium alloys, and nickel-based alloys, where standard HSS might wear too quickly.

3. Powder Metallurgy (PM)

Powder metallurgy taps are made using fine-grained metal powders, resulting in a more uniform microstructure. This gives them superior toughness and wear resistance compared to traditional HSS. PM taps perform exceptionally well in demanding applications such as tapping abrasive or high-tensile materials.

4. Solid Carbide

Solid carbide taps offer outstanding hardness and heat resistance, maintaining performance even at very high cutting speeds. They are best suited for mass production and high-precision CNC operations where tool deflection must be minimised. However, carbide taps are more brittle, so they are not ideal for manual or interrupted cutting operations.

Common Tap Coatings

• Titanium Nitride (TiN)

This gold-colored coating improves wear resistance and reduces friction between the tap and the workpiece. TiN-coated taps are versatile and ideal for a wide range of materials.

• Titanium Carbonitride (TiCN)

TiCN coatings provide even greater hardness and lubricity than TiN. They are especially beneficial when tapping harder materials like stainless steel or high-strength alloys.

• Titanium Aluminium Nitride (TiAlN)

TiAlN coatings offer excellent oxidation resistance and heat stability. This makes them perfect for high-speed tapping under dry or semi-dry cutting conditions.

• Diamond-Like Carbon (DLC)

DLC coatings deliver extreme smoothness and low friction, helping to reduce heat buildup and extend tap life. They are commonly used for aluminium and non-ferrous metals.

• Oxide Coating (Steam Tempered)

This black oxide finish helps retain cutting fluids on the tap surface, improving lubrication and chip evacuation. It's a cost-effective option for general-purpose use.

Tap Sizes, Thread Standards, and Hole Preparation

Before performing any tapping operation, understanding tap sizes, thread standards, and hole preparation is essential. The accuracy of these factors determines whether the thread will fit correctly and whether the tap will perform efficiently without breaking or wearing prematurely.

1. Tap Sizes and Thread Pitch

Taps come in a variety of sizes that correspond to specific thread diameters and pitches. The thread pitch refers to the distance between adjacent threads, and it varies depending on the thread type and standard. Selecting the correct tap size ensures that the threaded hole matches the screw or bolt precisely.

Common examples include:

M6 × 1.0 – Metric thread with a 6 mm diameter and 1.0 mm pitch.

¼-20 UNC – Unified Coarse thread with ¼ inch diameter and 20 threads per inch.

⅜-16 UNC – Common for general industrial fasteners.

When choosing a tap size, machinists typically use tap drill charts to determine the appropriate drill size before tapping. This ensures that the hole diameter is slightly smaller than the desired thread's minor diameter, allowing the tap to cut clean, accurate threads.

2. Thread Standards

Taps are produced according to international thread standards, which define dimensions, tolerances, and thread geometry. Understanding these standards helps ensure compatibility across parts and assemblies in different regions or industries.

Common thread standards include:

Metric (M) – The most widely used standard worldwide. Metric threads are specified by diameter and pitch, e.g., M8 × 1.25.

UNC (Unified National Coarse) – Common in North America, used for general-purpose fastening.

UNF (Unified National Fine) – Features finer threads for better strength in thin materials.

NPT (National Pipe Tapered) – Used for pressure-tight sealing in plumbing and pneumatic systems.

BSP (British Standard Pipe) – Similar to NPT but uses different angle geometry; common in the UK and Commonwealth countries.

Trapezoidal and ACME Threads – Used in power transmission and lead screws where high load capacity is required.

Each standard has specific applications, so choosing the correct one depends on the workpiece's design, assembly requirements, and regional manufacturing norms.

3. Hole Preparation Before Tapping

Proper hole preparation is critical to successful tapping. An incorrect hole size or poor surface condition can lead to tap breakage, poor thread quality, or excessive wear.

Key preparation steps include:

Drilling the Correct Hole Size: Always use a tap drill size recommended by tap drill charts for your thread type and pitch.

Chamfering the Hole Entrance: A small chamfer helps guide the tap into the hole smoothly and prevents cross-threading.

Deburring and Cleaning: Remove chips, burrs, and oil residues to ensure precise thread cutting.

Lubrication: Use appropriate cutting fluid to reduce friction and heat buildup. Proper lubrication extends tap life and ensures smoother cutting action.

Checking Alignment: Ensure the tap is perpendicular to the surface to prevent crooked threads or tool breakage.

By carefully following these preparation steps, machinists can achieve accurate, high-quality threads and maximise tool performance.

Common Problems in Tapping and How to Prevent Them

Even with the right tap and setup, tapping operations can still face challenges. Understanding the common problems in tapping and how to prevent them is essential for maintaining productivity, reducing tool costs, and ensuring consistent thread quality. Below are some of the most frequent issues machinists encounter and practical solutions to fix them.

1. Tap Breakage

Problem:

Tap breakage is one of the most common and costly issues in machining. It often occurs due to excessive torque, poor alignment, or inadequate lubrication.

When a tap breaks inside a hole, removing it can be difficult, sometimes resulting in scrapped parts.

Causes:

Hole size too small for the thread.

Incorrect feed or speed settings.

Poor chip evacuation in blind holes.

Misalignment between the tap and the hole.

Lack of proper cutting fluid.

Solutions:

Always use the correct tap drill size and check with a drill chart.

Apply proper lubrication according to material type.

Use spiral flute taps for blind holes to improve chip removal.

Ensure the tap is aligned correctly with the hole axis.

For CNC, use rigid tapping mode to synchronise spindle speed and feed rate.

2. Poor Thread Quality

Problem:

Threads may appear rough, undersized, or incomplete, leading to poor fit and reduced mechanical strength.

Causes:

Worn or dull tap cutting edges.

Incorrect tap material or coating for the workpiece.

Wrong cutting speed or feed rate.

Chips clogging the flutes.

Insufficient lubrication.

Solutions:

Replace worn taps regularly and inspect edges under magnification.

Match tap material and coating to workpiece type (e.g., TiCN-coated tap for stainless steel).

Maintain appropriate cutting speed - not too fast for tough materials.

Use compressed air or coolant to clear chips effectively.

Check for the correct hole diameter and thread standard.

3. Chip Packing and Jamming

Problem:

Chips may pack into the flutes during cutting, especially in blind holes, causing friction and possible tool breakage.

Causes:

Using straight flute taps in blind holes.

Lack of coolant or poor chip evacuation.

Ductile materials like aluminium or copper stick to flutes.

Solutions:

Choose spiral flute taps to lift chips out of blind holes.

Apply cutting fluid to reduce chip adhesion.

Use compressed air or coolant flushing for chip removal.

Reduce feed slightly to allow smoother chip flow.

4. Tap Chipping or Edge Wear

Problem:

Cutting edges become chipped or worn prematurely, leading to inconsistent thread quality and increased torque.

Causes:

Hard or abrasive materials.

Using uncoated taps at high speeds.

Excessive cutting force due to incorrect hole size.

Inadequate lubrication.

Solutions:

Use PM or carbide taps with advanced coatings (TiAlN or TiCN).

Reduce cutting speed for hard materials.

Drill the correct hole diameter to reduce cutting load.

Maintain a steady, controlled feed rate to prevent vibration.

5. Incorrect Thread Depth or Pitch

Problem:

Threads may not reach the required depth or have an incorrect pitch, leading to assembly issues or weak fastening.

Causes:

Feed not synchronised with spindle rotation in CNC tapping.

Wrong tap depth setting.

Using worn or incorrect tap geometry.

Solutions:

Use rigid tapping mode in CNC for perfect feed synchronisation.

Double-check program parameters and tool offset.

Replace old taps that have lost pitch accuracy.

Conclusion

Tapping is a fundamental operation in machining, playing a crucial role in producing accurate and durable internal threads for a wide range of industrial applications. From hand taps used in manual operations to high-performance spiral flute and forming taps used in CNC machines, each type of tap is designed to meet specific requirements based on material, hole type, and thread precision.

By understanding the different tap types, coating options, and cutting vs. forming principles, machinists and manufacturers can make better tool selections, improve threading efficiency, and extend tool life. Proper tap selection not only enhances thread quality but also reduces machine downtime and overall production costs.

At GreatCNC Machine, we provide high-quality CNC tapping solutions and a complete range of machining tools designed for precision, durability, and reliability. Whether you're working with steel, aluminium, or non-ferrous materials, our tapping tools and CNC machines ensure consistent results with every thread.

FAQ

1. What is the difference between a tap and a die?

A tap is used to cut internal threads inside a hole, while a die is used to cut external threads on rods or shafts. In simple terms, taps make threads for bolts to screw into, and dies make threads on bolts themselves. Both tools are essential in thread manufacturing and are often used together in repair and production work.

2. What are the main types of taps used in machining?

The most common types of taps include:

Hand taps (straight flute) – for general-purpose manual threading.

Spiral point taps (gun taps) – for through holes.

Spiral flute taps – for blind holes.

Form taps (roll taps) – for chip-free threading in ductile materials.

Pipe taps (NPT, BSPT) – for sealing threads in fluid or gas systems.

Machine taps (CNC taps) – designed for high-speed production environments.

Each type has its specific geometry and chip control suited to different materials and hole conditions.

3. How do I choose the right tap for my material?

The best tap depends on the material's hardness, ductility, and hole type:

Use HSS or cobalt taps for steel and stainless steel.

Use form taps for aluminium, copper, and brass.

Use carbide taps for hard or abrasive materials.

Apply coatings like TiN, TiCN, or TiAlN for longer tool life and smoother threading.

When in doubt, consult the tap manufacturer's chart or technical data for recommended tap type and speed settings.

4. What causes a tap to break, and how can I prevent it?

Tap breakage often results from:

Using the wrong hole size.

Poor lubrication or chip evacuation.

Misalignment during tapping.

Overly high cutting torque or speed.

To prevent this, use rigid tapping for CNC machines, select the right tap geometry for the material, and always apply adequate cutting fluid.

5. What's the difference between cutting taps and forming taps?

Cutting taps remove material to form threads and generate chips.

Forming taps (roll taps) displace the material to shape threads without cutting, so they produce no chips.

Forming taps are stronger, create smoother threads, and are ideal for ductile materials, while cutting taps are more versatile for hard or brittle materials.

6. How do I remove a broken tap?

Removing a broken tap can be tricky. Common methods include:

Using a tap extractor with fingers that grip the flutes.

Applying EDM (Electrical Discharge Machining) to dissolve the tap.

Use chemical tap removers for smaller or delicate parts.

Always ensure proper lubrication and hole cleaning before attempting to re-tap.

7. Do taps require different coatings for different materials?

Yes. Coatings enhance tool life and reduce friction:

TiN (gold) for general-purpose use.

TiCN (blue-grey) for hard materials and stainless steel.

TiAlN (purple-grey) for high-temperature or dry cutting.

DLC (diamond-like carbon) for non-ferrous metals like aluminium.

Choosing the right coating improves surface finish and prevents chip welding.

8. How long should a tap last?

Tap life depends on many factors - material type, cutting speed, lubrication, and production volume.

Generally:

HSS taps: up to 500–1000 holes.

Cobalt taps: 2–3 times longer.

Carbide taps: 5–10 times longer in stable CNC setups.

Monitoring torque or thread quality helps determine when to replace a tap before it breaks.