Twist drill bit specifications and dimensions?

A twist drill bit is one of the most essential cutting tools in manufacturing, construction, woodworking, metalworking, and DIY projects. Its primary function is to create cylindrical holes in a wide range of materials, including metal, wood, plastic, concrete, and composites. The design of a twist drill bit—characterized by helical flutes that spiral around the shaft—allows for efficient chip removal, cooling, and guidance during drilling. To understand twist drill bits thoroughly, it is crucial to explore their specifications, dimensions, leading brands, and popular models, as these factors directly impact performance, precision, and suitability for specific applications.

Core Specifications of Twist Drill Bits

Twist drill bits are defined by a set of key specifications that determine their functionality, compatibility with tools, and performance on different materials. These specifications include material composition, coating type, flute design, shank type, point angle, and helix angle. Each specification plays a unique role in how the drill bit interacts with the workpiece and the drilling equipment.

Material Composition

The material of a twist drill bit is a critical factor in its durability, hardness, and heat resistance. Common materials used in twist drill bit manufacturing include:

 

  • High-Speed Steel (HSS): HSS is the most widely used material for twist drill bits due to its balance of affordability, toughness, and heat resistance. HSS drill bits can withstand temperatures up to 600°C (1,112°F) and are suitable for drilling mild steel, aluminum, copper, wood, and plastic. They are less brittle than carbide, making them ideal for general-purpose use.
  • HSS-Co (Cobalt-Alloyed HSS): HSS-Co drill bits contain 5-8% cobalt, which enhances their heat resistance (up to 700°C/1,292°F) and hardness. This makes them suitable for drilling harder materials such as stainless steel, cast iron, and high-alloy steels. The cobalt content also improves wear resistance, extending the bit’s lifespan under heavy use.
  • Carbide (Tungsten Carbide): Carbide drill bits are made from tungsten carbide particles bonded with a cobalt matrix. They offer exceptional hardness (up to 90 HRC on the Rockwell scale) and heat resistance (up to 1,000°C/1,832°F), making them ideal for drilling extremely hard materials like hardened steel, ceramics, concrete, and composites. However, carbide is brittle, so these bits require careful handling to avoid chipping or breaking.
  • Cobalt Carbide (Carbide-Tipped): Carbide-tipped drill bits have a carbide cutting edge welded to an HSS shank. This design combines the toughness of HSS with the wear resistance of carbide, making them suitable for drilling abrasive materials like fiberglass, tile, and cast iron without sacrificing durability.
  • Powder Metallurgy HSS (PM-HSS): PM-HSS drill bits are manufactured using powder metallurgy techniques, resulting in a more uniform grain structure. This enhances their hardness, toughness, and wear resistance compared to conventional HSS. PM-HSS bits are ideal for high-speed drilling and applications involving hard or abrasive materials.

Coating Type

Coatings are applied to twist drill bits to reduce friction, improve heat dissipation, prevent chip adhesion, and extend tool life. Common coatings include:

 

  • TiN (Titanium Nitride): A gold-colored coating that reduces friction and wear. TiN-coated bits are suitable for drilling steel, aluminum, and wood, offering better performance than uncoated HSS bits.
  • TiCN (Titanium Carbonitride): A darker gray coating with higher hardness and wear resistance than TiN. TiCN coatings are ideal for high-speed drilling of steel and cast iron, as they reduce heat buildup and improve chip flow.
  • TiAlN (Titanium Aluminum Nitride): A purple or blue coating that provides excellent heat resistance (up to 800°C/1,472°F) and oxidation resistance. TiAlN-coated bits are perfect for drilling stainless steel, high-alloy steels, and other high-temperature applications.
  • AlCrN (Aluminum Chromium Nitride): A black coating with superior resistance to high temperatures and oxidation. AlCrN-coated bits excel in drilling heat-resistant alloys, titanium, and nickel-based superalloys, common in aerospace and automotive industries.
  • Zirconium Nitride (ZrN): A silver-colored coating that offers good lubricity and corrosion resistance. ZrN-coated bits are often used for drilling non-ferrous metals like aluminum and copper.

Flute Design

Flutes are the spiral grooves on the drill bit that facilitate chip removal and coolant flow. The number, size, and helix angle of flutes vary based on the application:

 

  • Number of Flutes: Most twist drill bits have 2 flutes, which balance chip removal and stability. However, 3-flute or 4-flute bits are available for specific tasks: 3-flute bits improve centering and reduce vibration in metal drilling, while 4-flute bits enhance chip evacuation in high-speed drilling of non-ferrous metals.
  • Flute Length: The flute length determines the maximum depth of the hole that can be drilled. Longer flutes are used for deep-hole drilling, while shorter flutes provide better rigidity for shallow holes.
  • Helix Angle: The helix angle (the angle between the flute and the bit’s axis) affects chip removal and cutting forces. A low helix angle (10-20°) is suitable for drilling hard materials like steel, as it reduces cutting pressure. A high helix angle (30-45°) is better for soft materials like wood and aluminum, as it promotes faster chip evacuation.

Shank Type

The shank is the non-cutting end of the drill bit that connects to the drilling tool (e.g., drill press, 手电钻，or milling machine). Shank type determines compatibility with tool chucks and adapters:

 

  • Straight Shank: The most common shank type, with a uniform diameter along its length. Straight shanks are compatible with 3-jaw chucks, which are standard on most handheld drills and drill presses. They are available in diameters up to 13mm (0.5 inches) for larger bits, though some heavy-duty models may have larger straight shanks.
  • Morse Taper Shank: Morse taper shanks have a tapered design that self-locks into matching tapered sockets, common in drill presses and milling machines. They are used for larger drill bits (typically 13mm/0.5 inches and above) to provide a secure, rigid connection that minimizes slippage during high-torque drilling. Morse tapers are standardized into sizes (MT1 to MT6), with larger numbers indicating larger shank diameters.
  • Hex Shank: Hexagonal shanks fit into hex chucks or quick-change adapters, providing better torque transmission and preventing slippage. They are popular in cordless drills and impact drivers, where quick bit changes are essential. Hex shanks are available in various sizes, including 1/4-inch, 3/8-inch, and 1/2-inch.
  • Reduced Shank: Reduced shank bits have a smaller shank diameter than the cutting diameter, allowing larger cutting diameters to fit into smaller chucks. For example, a 20mm cutting diameter bit may have a 13mm straight shank, enabling use with a 13mm chuck.

Point Angle

The point angle is the angle formed by the two cutting edges at the tip of the drill bit. It determines the bit’s ability to penetrate the material and the quality of the hole:

 

  • 118° Point Angle: The standard angle for general-purpose drilling. It works well for drilling mild steel, aluminum, copper, and wood, balancing penetration speed and hole accuracy.
  • 135° Split Point Angle: A self-centering angle with a chisel edge reduced to minimize walking (drifting off-center) on hard materials. 135° bits are ideal for stainless steel, cast iron, and high-alloy steels, providing better precision and reducing cutting forces.
  • 90°-110° Point Angle: Used for drilling soft materials like wood, plastic, and aluminum. The sharper angle allows for faster penetration and cleaner holes in low-density materials.
  • 140°-150° Point Angle: Designed for drilling hard, brittle materials like ceramics, glass, and hardened steel. The larger angle distributes cutting forces more evenly, reducing the risk of chipping.

Dimensions of Twist Drill Bits

Twist drill bit dimensions are standardized to ensure compatibility with tools and workpieces. The key dimensional parameters include diameter, overall length, flute length, shank diameter, and web thickness. These dimensions are specified in both metric (millimeters) and imperial (inches) units, depending on regional standards.

Diameter

The diameter of a twist drill bit is the most critical dimension, as it determines the size of the hole it creates. Diameters range from micro-sized bits (less than 0.5mm) for precision drilling to large bits (over 100mm) for heavy-duty applications.

 

  • Metric Diameters: Common metric sizes start at 0.5mm and increase in increments of 0.1mm (e.g., 0.5mm, 0.6mm, …, 1.0mm), then 0.25mm (e.g., 1.25mm, 1.5mm, …, 5.0mm), and larger increments for bigger bits (e.g., 5mm, 6mm, …, 20mm, 25mm).
  • Imperial Diameters: Imperial sizes are specified in fractions of an inch (e.g., 1/16 inch, 1/8 inch, 3/16 inch, …, 1 inch) or decimal inches (e.g., 0.0625 inch, 0.125 inch). Smaller imperial bits may also use gauge numbers (e.g., #80 to #1, where lower numbers indicate larger diameters).

Overall Length (OAL)

The overall length is the total length of the drill bit from the tip of the cutting edge to the end of the shank. It varies based on the bit’s intended use:

 

  • Jobber Length: The standard length for general-purpose drill bits. Jobber length bits have an overall length approximately 9-14 times their diameter. For example, a 6mm diameter jobber bit typically has an overall length of 90mm, while a 12mm bit may be 150mm long.
  • Stub Length: Shortened bits designed for high rigidity and precision. Stub length bits have an overall length of 3-6 times their diameter, making them ideal for drilling in tight spaces or where minimal deflection is required. A 6mm stub bit may have an overall length of 30mm.
  • Taper Length: Extra-long bits used for deep-hole drilling. Taper length bits have an overall length 15-20 times their diameter, with flutes extending most of the length. A 6mm taper length bit can be up to 120mm long.
  • Screw-Machine Length: Similar to stub length but even shorter, with an overall length of 2-3 times their diameter. These bits are used in screw machines for high-speed, repetitive drilling of small holes.

Flute Length

Flute length is the portion of the drill bit’s length that contains the helical flutes, responsible for chip removal. It is typically slightly shorter than the overall length (excluding the shank). For jobber length bits, flute length is around 7-12 times the diameter, ensuring sufficient chip evacuation for standard drilling depths.

Shank Diameter

Shank diameter varies based on the shank type:

 

  • Straight Shank: For bits up to 13mm in diameter, the shank diameter is usually equal to the cutting diameter. Larger straight shank bits may have a reduced shank (e.g., a 16mm cutting diameter bit with a 13mm shank).
  • Morse Taper Shank: Morse taper shank diameters are standardized by size: MT1 (6.35mm), MT2 (12.7mm), MT3 (19.05mm), MT4 (25.4mm), MT5 (31.75mm), and MT6 (38.1mm).
  • Hex Shank: Common hex shank sizes include 6.35mm (1/4 inch), 9.525mm (3/8 inch), and 12.7mm (1/2 inch), corresponding to standard chuck sizes.

Web Thickness

The web is the central, unfluted portion of the drill bit that connects the flutes. Web thickness increases with the bit’s diameter to provide strength. Thicker webs improve rigidity but can increase cutting forces, so some bits feature a web-thinning design (reducing web thickness near the tip) to lower penetration resistance.

Leading Brands of Twist Drill Bits

Numerous manufacturers produce twist drill bits, each offering unique features, quality levels, and product lines tailored to different applications—from DIY home projects to industrial manufacturing. Below are some of the most reputable brands, along with their key characteristics and popular models.

Bosch

Bosch is a German multinational engineering and technology company known for its high-quality power tools and accessories. Bosch twist drill bits are celebrated for their precision, durability, and versatility, catering to both professional and DIY users.

 

  • Key Features: Bosch bits often use premium HSS or HSS-Co materials with advanced coatings like TiAlN or TiCN. They feature optimized flute designs for efficient chip removal and split points to prevent walking.
  • Popular Models:
    • Bosch Professional HSS-R Drill Bits: A general-purpose line made from HSS with a TiN coating. Available in metric sizes from 1mm to 13mm, these bits are suitable for drilling steel, aluminum, wood, and plastic. The 5mm model (article number 2608585208) is a bestseller, with a jobber length of 85mm and a 118° point angle.
    • Bosch Professional HSS-Co 8% Drill Bits: Designed for hard materials like stainless steel and cast iron. These bits contain 8% cobalt and feature a TiAlN coating for heat resistance. The 8mm model (article number 2608585325) has a Morse taper shank (MT2), jobber length of 120mm, and a 135° split point.
    • Bosch MultiConstruction Drill Bits: Carbide-tipped bits for drilling masonry, concrete, metal, and wood. The 6mm model (article number 2608680575) features a hex shank for quick changes, a 130° point angle, and a flute design that works across multiple materials.

DeWalt

DeWalt, a subsidiary of Stanley Black & Decker, is a leading brand in professional power tools and accessories. DeWalt twist drill bits are engineered for heavy-duty use, with a focus on durability and performance in industrial settings.

 

  • Key Features: DeWalt bits often use PM-HSS or HSS-Co materials with proprietary coatings like Black Oxide or TiAlN. They include features like parabolic flutes for faster chip removal and 3-flute designs for stability in metal drilling.
  • Popular Models:
    • DeWalt DW1177 HSS Drill Bit Set: A 29-piece set with sizes from 1/16 inch to 1/2 inch. The bits are made from HSS with a black oxide coating to reduce corrosion and improve lubricity. The 1/4-inch bit in the set has a jobber length of 3-3/4 inches and a 118° point angle.
    • DeWalt DWA1240 HSS-Co 5% Drill Bits: For drilling stainless steel and high-alloy steels. These bits contain 5% cobalt and feature a TiAlN coating. The 3/8-inch model has a straight shank, jobber length of 4-1/2 inches, and a 135° split point, ideal for high-speed drilling.
    • DeWalt DWA5820 Carbide Drill Bits: Solid carbide bits for extreme hardness applications, such as hardened steel and ceramics. The 5mm model has a straight shank, stub length of 25mm, and a 140° point angle for precise, chip-free drilling.

Makita

Makita is a Japanese manufacturer renowned for its power tools and accessories, known for their precision and reliability. Makita twist drill bits are popular among professionals in woodworking, metalworking, and construction.

 

  • Key Features: Makita bits use high-grade HSS, HSS-Co, or carbide materials with coatings like TiCN or ZrN. They feature ergonomic shank designs for secure chuck grip and optimized helix angles for material-specific performance.
  • Popular Models:
    • Makita B-65599 HSS Drill Bit Set: A 10-piece metric set with sizes from 3mm to 10mm. Made from HSS with a TiCN coating, these bits have jobber lengths (e.g., 3mm = 65mm, 10mm = 130mm) and 118° point angles, suitable for steel and aluminum.
    • Makita B-65874 HSS-Co 8% Drill Bits: Designed for stainless steel and cast iron, these bits have an 8% cobalt content and a TiAlN coating. The 12mm model has a Morse taper shank (MT2), jobber length of 160mm, and a 135° split point for reduced walking.
    • Makita D-46493 Carbide Tipped Drill Bits: Carbide-tipped bits for masonry and metal. The 8mm model features a hex shank, overall length of 100mm, and a 130° point angle, making it versatile for drilling brick, concrete, and steel.

Guhring

Guhring is a German precision tool manufacturer specializing in high-performance cutting tools for industrial applications. Guhring twist drill bits are known for their exceptional accuracy, long tool life, and suitability for demanding manufacturing environments.

 

  • Key Features: Guhring bits use advanced materials like PM-HSS and carbide with proprietary coatings like AlCrN. They feature precision-ground flutes, optimized point geometries, and internal coolant holes for deep-hole drilling.
  • Popular Models:
    • Guhring 800 Series HSS Drill Bits: A general-purpose industrial line made from PM-HSS with a TiN coating. Available in metric sizes from 0.5mm to 20mm, these bits have jobber lengths and 118° point angles, ideal for high-speed drilling of steel and non-ferrous metals. The 6mm model (order number 800 06,00) has a straight shank and flute length of 50mm.
    • Guhring 802 Series HSS-Co 5% Drill Bits: Designed for hard steels and alloys, these bits contain 5% cobalt and feature a TiAlN coating. The 10mm model (order number 802 10,00) has a Morse taper shank (MT2), jobber length of 140mm, and a 135° split point with web thinning for reduced cutting forces.
    • Guhring 930 Series Carbide Drill Bits: Solid carbide bits for high-precision drilling of hardened materials. The 4mm model (order number 930 04,00) has a straight shank, stub length of 30mm, and a 140° point angle, suitable for aerospace and automotive applications.

Sandvik Coromant

Sandvik Coromant, a division of the Swedish Sandvik Group, is a global leader in metal-cutting tools. Their twist drill bits are engineered for efficiency, precision, and sustainability in industrial metalworking.

 

  • Key Features: Sandvik Coromant bits use advanced carbide grades and PM-HSS with coatings like TiAlN and AlCrN. They incorporate innovative designs such as unequal flute spacing to reduce vibration and improve surface finish.
  • Popular Models:
    • Sandvik Coromant CoroDrill 860: A versatile carbide drill bit for steel, stainless steel, and cast iron. Available in diameters from 3mm to 20mm, it features a 140° point angle, internal coolant holes, and a TiAlN coating. The 8mm model has a straight shank, jobber length of 110mm, and is optimized for high-feed drilling.
    • Sandvik Coromant CoroDrill 300: An HSS-Co drill bit for general metal drilling. With 5% cobalt content and a TiCN coating, it offers excellent wear resistance. The 12mm model has a Morse taper shank (MT3), jobber length of 180mm, and a 135° split point for stability.
    • Sandvik Coromant CoroDrill 600: A micro-drill bit for precision holes in electronics and medical devices. The 1mm model has a straight shank, stub length of 15mm, and a 130° point angle, made from ultra-fine carbide for accuracy.

Irwin Tools

Irwin Tools, a subsidiary of Stanley Black & Decker, is a well-known brand for hand tools and power tool accessories, with a focus on accessibility and reliability for DIY users and professionals.

 

  • Key Features: Irwin bits use HSS and HSS-Co materials with coatings like Black Oxide and TiN. They are designed for ease of use, with features like self-centering points and universal shanks compatible with most drills.
  • Popular Models:
    • Irwin 3018002 HSS Drill Bit Set: A 20-piece set with sizes from 1/16 inch to 1/2 inch. The bits are made from HSS with a black oxide coating and have 118° point angles. The 3/8-inch bit in the set has a jobber length of 4 inches and a straight shank.
    • Irwin 3018012 Cobalt Drill Bit Set: A 12-piece set for stainless steel and hard metals, containing 5% cobalt. The bits feature a TiAlN coating and 135° split points. The 1/4-inch model has a jobber length of 3-1/2 inches and a straight shank.
    • Irwin Unibit Step Drill Bits: While not traditional twist bits, these multi-step bits are popular for drilling variable hole sizes in metal and plastic. The 3/16-inch to 7/8-inch model (10234) has a hex shank, 135° point angle, and is made from HSS with a TiN coating.

Specialized Twist Drill Bits for Specific Applications

Beyond general-purpose bits, there are specialized twist drill bits designed for unique materials or applications. These bits incorporate modified specifications and dimensions to address the challenges of specific drilling tasks.

Wood Drilling Bits

Wood drill bits require high helix angles (30-45°) to quickly remove wood chips and prevent clogging. They often have sharp, 90°-110° point angles for fast penetration.

 

  • Brands and Models:
    • Bosch Professional Wood Drill Bits (2608585405): 8mm diameter, high helix angle (35°), jobber length 150mm, TiN coating to reduce friction in softwoods and hardwoods.
    • DeWalt DW1587 Spade Drill Bits: 1/2-inch diameter, flat spade tip for large holes in wood, hex shank, and 12-inch overall length for deep drilling.

Masonry Drill Bits

Masonry bits are carbide-tipped with a chisel-like point to break through concrete, brick, and stone. They have a reduced helix angle (5-15°) to handle abrasive materials.

 

  • Brands and Models:
    • Makita D-46484 Masonry Drill Bits: 10mm diameter, carbide tip, hex shank, 160mm overall length, optimized for concrete and brick.
    • Bosch Professional BlueGranite Masonry Bits: 12mm diameter, SDS-plus shank for hammer drills, 210mm length, and wear-resistant carbide tip.

Metal Drilling Bits for High-Alloy Steels

High-alloy steels require HSS-Co or carbide bits with TiAlN coatings and 135° split points to minimize heat and vibration.

 

  • Brands and Models:
    • Guhring 802 HSS-Co 8% Drill Bits: 15mm diameter, Morse taper shank (MT3), jobber length 200mm, TiAlN coating, ideal for Inconel and other superalloys.
    • Sandvik Coromant CoroDrill 860 Carbide Bits: 10mm diameter, internal coolant holes, 140° point angle, designed for high-speed drilling of stainless steel.

Micro-Drill Bits

Micro-drill bits (diameters <3mm) are used in electronics, medical devices, and jewelry making, requiring extreme precision and rigidity.

 

  • Brands and Models:
    • Sandvik Coromant CoroDrill 600: 0.5mm diameter, stub length 10mm, ultra-fine carbide, straight shank, used for drilling circuit boards.
    • Guhring Micro-Drill Bits (930 Series): 1mm diameter, PM-HSS material, TiN coating, 130° point angle, suitable for precision metalworking.

Conclusion

Twist drill bits are indispensable tools with a wide range of specifications, dimensions, and designs tailored to diverse applications. Understanding their material composition, coating, flute design, shank type, and dimensions is crucial for selecting the right bit for the job. Leading brands like Bosch, DeWalt, Makita, Guhring, and Sandvik Coromant offer models ranging from general-purpose HSS bits to specialized carbide bits for extreme materials. By matching the bit’s specifications to the material, drilling tool, and hole requirements, users can ensure optimal performance, precision, and tool longevity. Whether for DIY projects, construction, or industrial manufacturing, the right twist drill bit is key to achieving efficient and accurate results.

 

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