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A 10 mm drill bit measures 0.3937 inches. The nearest common fractional size is 25/64 inch, but it measures 0.3906 inches—about 0.0031 inch (0.078 mm) smaller. Use a 10 mm bit when the specified diameter matters; treat 25/64 inch as an approximation only when that small difference is acceptable.
10 mm drill bit conversion
To convert millimetres to inches, divide by 25.4, since 1 inch equals 25.4 mm. For a 10 mm bit, 10 ÷ 25.4 = approximately 0.3937 inches. The conversion reference lists the nominal size as 10.000 mm, or 0.3937 inches (ShopMath).
Is 25/64 inch the same as 10 mm?
No. The nearest common fractional drill size listed for 10 mm is 25/64 inch, which measures 0.3906 inches (UK Drills). Compared with 10 mm (0.3937 inches), it is about 0.0031 inch, or 0.078 mm, smaller. It is a nearby substitute, not an exact equivalent.
| Nominal drill size | Decimal inches | Difference from 10 mm |
|---|---|---|
| 10 mm | 0.3937 in | Exact nominal metric size |
| 25/64 in | 0.3906 in | About 0.0031 in (0.078 mm) smaller |
Which bit should you use?
- Choose 10 mm when a plan, fitting, or specification calls for a 10 mm hole and the nominal diameter matters.
- Consider 25/64 inch only if the application allows a slightly smaller hole. Check the fit or specification rather than assuming the sizes are interchangeable.
Why the finished hole may differ from the bit size
A bit’s marking gives its nominal diameter, not a guarantee that the finished hole will measure exactly that size. Bit wear, run-out, and the material being drilled can affect the cut. Account for the operation and material when a close-tolerance hole is required.
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#1 Best Overall
10mm Metric M35 Cobalt Steel Extremely Heat Resistant Twist Drill Bit of 1pcs with Straight Shank to Cut Through Hard Metals Such as Stainless Steel and Cast Iron, 5% Cobalt M35 Grade HSS-CO
- Cobalt Steel - Manufactured From M35 5% Cobalt Steel, With Molybdenum And Cobalt Added To Creates A Hardened Alloy, Measuring Rockwell Hardness Up To 65, For Much Faster Cutting And Extra Longer Life Span, With Up To 10 Times When Compared with an Average HSS Drill Bit.
- HSS Titanium Coating - Classic HSS Construction With Titanium Coating For Capability And Durability. The Cutting Edge Is Hardened And Honed For Sharpness.
- Flutes Form - 2 Flutes Form Helps Clear Chips And Debris Away From The Bit, Decreasing Friction And Heat For A Faster, Cooler Drilling Process, Chatter-Free Design With Staggered Cutting Teeth Ensure The Precise Countersinking And Hole Smooth Clean.
- Straight Shank And 135° Point Angle - Straight Shank For Standard Drill Chucks And Collet Chuck To Hold Firmly, Assuring Accurate Centering; Helical Flute For Swarf To Easily Get Out; Ideal For General Purpose Drilling Applications.
- For Metalworking - Particularly Successful In Cutting Through Hard Metals(Hardness Less Than Hrc38°) Such As Stainless Steel And Cast Iron, Although They Can Be Used For Softer Materials Like Copper And Aluminium, Too. Not For Hardened Steel And High Carbon Steel.
For tapping, use the thread specification
A 10 mm conversion alone does not determine the right tap-drill size. Tapping requires the thread specification and a matching tap-drill chart; the nearest inch fraction is not a substitute for that information.
Quick Recap
Bestseller No. 3
Bestseller No. 4
Bestseller No. 5
Best Value
METALLIXITY Drill Bit (10mm) 4341 High-Speed Steel Black & Gold 1Pcs
- [1]: APPLY TO - The drill bit is suitable for daily equipment maintenance and repair, low-intensity applications, and medium to low-hardness metals, including common stainless steel, steel, aluminum alloy, and copper. It is also effective for drilling wood and plastic materials, making it an excellent choice for various DIY projects around the home.
- [2]: SPECIFICATION - The drill bit has a cutting diameter of 10mm, a shank diameter of 10mm, a flute length of 90mm/3.54 inches, an overall length of 130mm/5.12 inches, and a 118-degree standard point tip.
- [3]: INSTRUCTION - Set the suitable speed according to the material's hardness and the drill bit diameter. Higher speeds can be used for softer materials, while lower speeds should be applied for harder materials. Please refer to the details provided on the product page.
- [4]: ADVANTAGE - The 4341 high-speed steel material has high hardness, good wear resistance, and toughness, enabling it to withstand significant impact without easily breaking. Black and gold finish can further enhance the drill bit's wear and corrosion resistance, thereby extending its service life.
- [5]: QUANTITY INCLUDED - Set contains 1pcs x 10mm twist drill bits, perfect for home use, repairs, and small manufacturing projects. (Notice: it is recommended to first drill a small guide hole before drill a larger hole)
Rank #4
Verkelly Brad Point Drill Bits, 10mm Dia x 119mm Length, 2 Pcs
- 【Premium Material】: Crafted from high-quality alloy steel materials, these brad point drill bits offer superior durability and performance, ensuring a reliable tool for your woodworking projects. The construction of these drill bits guarantees long-lasting usage without compromising on quality.
- 【Optimized Cutting Efficiency】: Experience enhanced cutting efficiency with our drill bits, featuring specialized designs that ensure fast and precise cutting of wood fibers before drilling. The optimized spurs and beveled edges lead to clean drilling without any deviation, providing smooth and accurate results every time.
- 【Versatile Usage】: The brad point drill bits are suitable for a wide range of applications, making them ideal for use in soft, hard, exotic woods, veneered, laminated wood, MDF, and even acrylic glass. With various sizes available, these drill bits cater to different woodworking needs, offering versatility and convenience for your projects.
- 【Precision and Durability】: Designed for precision and longevity, the drill bits feature brad-point tips that provide pinpoint accuracy for starting drilling holes. The inclusion of titanium coatings enhances wear resistance, temperature tolerance, and overall durability, ensuring that these drill bits can withstand demanding woodworking tasks while maintaining high performance levels.
- 【About us】: Our store is dedicated to providing a comprehensive selection of reliable and durable hardware solutions to meet all your needs. With our unwavering commitment to excellence, you can trust us to deliver top-quality products that stand the test of time. We appreciate your interest and support.
Rank #3
10mm Straight Shank Drill Bits 2pcs 4341 High-Speed Stee
- High Speed Steel Tool: The 4341 High-speed steel straight shank tool material has high hardness, And its wear resistance and corrosion resistance further extend its service life.
- Drill Bit Size: The drill bit Cutting Edge Diameter : 10mm / 0.39inches; Shank Diameter : 10mm / 0.39inches; Cutting Edge Length: 90mm / 3.54inches; overall length of 130mm/5.12 inches
- Feature & Finish: Gold titanium and black nitride dual Finish coating enhances the drill bit's wear and corrosion resistance, Enable it to withstand significant impacts without easily breaking.
- Sharp Spiral Flutes: Provide clean and smooth cutting. High cutting edge strength and fast cutting speed. For thick materials, multiple drilling should be carried out, The spiral groove facilitates the export of metal shavings, saving operation time.
- Versatile Uses: Drill bits are suitable for daily equipment maintenance and repair, low strength applications, and low to medium hardness metals, including stainless steel, iron, copper, brass, aluminum alloy, as well as plastics and wood.
Rank #2
Hymnorq 8-Piece Metric HSS Drill Bit Set for Wood and Plastic, 3mm-10mm
- ESSENTIAL SIZES & ORGANIZED CASE: Includes 8 frequently used metric whole-number sizes: 3, 4, 5, 6, 7, 8, 9, and 10mm. Neatly organized in a durable, bright yellow plastic indexed storage case for easy transportation, secure storage, and instant size identification.
- BREAK-RESISTANT & HAND-DRILL FRIENDLY: Manufactured using a hot roll-forged process, these bits retain their continuous metal grain structure. This provides superior toughness and flexibility, allowing them to absorb the slight side-loads and wobbles typical of standard hand drills without easily snapping.
- OPTIMIZED FOR SOFT MATERIALS: Crafted from High-Speed Steel (HSS) 4241, these bits are specifically designed for efficient, clean drilling into wood, plastics, PVC, and thin/soft metal sheets like aluminum. (Note: Not recommended for hard steel, thick iron plates, or masonry).
- ANTI-RUST GOLD FINISH: Featuring a decorative gold-toned coating that effectively prevents rust and extends the shelf life of the bits. This protective finish provides excellent corrosion resistance, ensuring your tools stay in great condition while sitting in your garage or toolbox.
- UNIVERSAL FIT & GREAT VALUE: Features a standard 118-degree point angle and straight round shank design for easy, secure attachment to all standard drill chucks. An incredibly cost-effective and reliable choice for general home maintenance, DIY projects, and everyday repairs.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
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