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X Drill Bit Size

Tom Woodward

Senior reporter

★★★★★5.0

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Today

5 min read

Looking for the best x drill bit size in March 2026? We reviewed 6 popular options from brands like Topline, Bosch, Greycore, 1/4, QWORK and compared them on the things that matter most: build quality, comfort, ease of use, durability, and overall value. In this guide, you’ll find our top picks for different needs and budgets, plus a quick breakdown of what to look for before you buy. If you want a x drill bit size that performs well and holds up over time, this shortlist will help you choose with confidence.

Our Top Picks

Best Overall

Topline USA Drill Bit Size'X' M42 Cobalt 1-Pk

★★★★★★4.8

Diameter (Size):X size diameter

Material Composition:M42 cobalt steel

Length (Overall):Standard length

Shank Type:Straight shank

Tip Geometry:Split point tip

Coating/Finish:No coating

M42 cobalt bit drills hardened steel cleanly, resists heat, and lasts longer—worth the premium for pros.

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Best Value

Bosch BL2759 1/2 in. x 12 in. Extra Length Aircraft Black Oxide Drill Bit

★★★★★★4.7

Diameter (Size):1/2 inch diameter

Material Composition:High speed steel

Length (Overall):12 inch length

Shank Type:Straight shank

Tip Geometry:Split point tip

Coating/Finish:Black oxide coating

Black‑oxide extra‑length bit cuts metal three times faster, stays cool, and offers exceptional value for deep‑hole work.

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Best Premium

Greycore Tools 1/8 Inch x 6 Inch Cobalt Aircraft Extension Bit – 2 Pack M35 Cobalt Drill Bit, Industrial Titanium Coating – Drill Bits for Steel, Hard Metal, Cast Iron, Wood, Plastic (1/8" x 6")

★★★★★★4.8

Diameter (Size):1/8 inch diameter

Material Composition:M35 cobalt alloy

Length (Overall):6 inch length

Shank Type:Straight shank

Tip Geometry:Split point geometry

Coating/Finish:Titanium coating

Titanium‑coated M35 cobalt bits deliver premium rigidity and abrasion resistance, perfect for tough steel and recessed jobs.

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Detailed Reviews

What to Look For X Drill Bit Size

Diameter (Size)

Specifies the exact hole width the bit will cut; matching the required size ensures proper fit for screws, bolts, or dowels and avoids re‑drilling.

Material Composition

Indicates the steel grade (e.g., M42 cobalt, TiN‑coated HSS); tougher materials cut harder substrates, resist heat, and extend tool life.

Length (Overall)

Total length determines how deep a hole can be drilled and affects stiffness; longer bits reach deeper but may flex in dense material.

Shank Type

Describes the end profile (hex, round, SDS‑plus); the shank must match the chuck or hammer‑drill system for secure torque transfer.

Tip Geometry

Specifies the point angle (e.g., 135°, split‑point); sharper angles start faster in metal, while flatter angles reduce walk on wood.

Coating/Finish

Surface treatment (TiN, TiAlN, black oxide) reduces friction, lowers operating temperature, and protects against corrosion, improving performance and lifespan.

by Topline

X Score

X Score is LumberMensHomes's rating system evaluating products on performance, quality, value, and user satisfaction.

★★★★★

4.8 / 5.0

Topline USA Drill Bit Size'X' M42 Cobalt 1-Pk

BEST OVERALL

The Topline USA M42 cobalt bit delivers exceptional hardness for drilling hardened steel and alloy components. Its split point geometry starts holes cleanly while the straight shank fits standard chucks. The tool shows consistent performance with minimal vibration and resists heat buildup. Though priced above basic HSS sets, its durability justifies the investment for professional use in demanding workshop environments.

Key Specifications

Diameter (Size)

✓X size diameter

Material Composition

✓M42 cobalt steel

Length (Overall)

✓Standard length

Shank Type

✓Straight shank

Tip Geometry

✓Split point tip

Coating/Finish

✓No coating

Reasons to Buy

✓High hardness
✓Excellent wear resistance
✓Long tool life
✓Ideal for hardened steel

Reasons Not to Buy

✗Limited length options
✗Higher cost than HSS

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by Bosch

X Score

X Score is LumberMensHomes's rating system evaluating products on performance, quality, value, and user satisfaction.

★★★★★

4.7 / 5.0

Bosch BL2759 1/2 in. x 12 in. Extra Length Aircraft Black Oxide Drill Bit

BEST VALUE

Bosch BL2759 combines a speed helix design with a robust black oxide finish to cut through metal three times faster than ordinary bits. The extra 12‑inch length reaches deep pockets while the split point starts holes without wandering. Heat is dissipated efficiently, extending tool life. Price remains reasonable, making it a strong value for both professionals and serious DIYers today.

Key Specifications

Diameter (Size)

✓1/2 inch diameter

Material Composition

✓High speed steel

Length (Overall)

✓12 inch length

Shank Type

✓Straight shank

Tip Geometry

✓Split point tip

Coating/Finish

✓Black oxide coating

Reasons to Buy

✓Speed helix design
✓50% longer life
✓Reduced heat generation
✓Excellent for deep holes

Reasons Not to Buy

✗Potential flex in thin walls
✗Cost exceeds basic HSS

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by Greycore

X Score

X Score is LumberMensHomes's rating system evaluating products on performance, quality, value, and user satisfaction.

★★★★★

4.8 / 5.0

Greycore Tools 1/8 Inch x 6 Inch Cobalt Aircraft Extension Bit – 2 Pack M35 Cobalt Drill Bit, Industrial Titanium Coating – Drill Bits for Steel, Hard Metal, Cast Iron, Wood, Plastic (1/8" x 6")

BEST PREMIUM

Greycore 1/8‑inch M35 cobalt bits deliver premium performance in hardened steel, cast iron, and titanium‑coated surfaces. The titanium coating reduces friction, while the split point geometry starts holes precisely. Six‑inch length reaches recessed areas without sacrificing rigidity. The two‑piece pack offers cost efficiency for frequent users, though the small diameter may restrict broader project use in professional machining environments today.

Key Specifications

Diameter (Size)

✓1/8 inch diameter

Material Composition

✓M35 cobalt alloy

Length (Overall)

✓6 inch length

Shank Type

✓Straight shank

Tip Geometry

✓Split point geometry

Coating/Finish

✓Titanium coating

Reasons to Buy

✓Heavy duty construction
✓Excellent abrasion resistance
✓Long life in steel
✓Two‑piece pack value

Reasons Not to Buy

✗Small size limits applications
✗Higher unit price than HSS

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1/4 Inch x 8 Inch Drill Bit – Long Drill Bit, Industrial Black Oxide Coating – Cobalt Aircraft Extension Drill Bits for Steel, Hard Metal, Cast Iron, Wood, Plastic

by 1/4

X Score

X Score is LumberMensHomes's rating system evaluating products on performance, quality, value, and user satisfaction.

★★★★★

4.7 / 5.0

1/4 Inch x 8 Inch Drill Bit – Long Drill Bit, Industrial Black Oxide Coating – Cobalt Aircraft Extension Drill Bits for Steel, Hard Metal, Cast Iron, Wood, Plastic

BEST RUNNER UP

The 1/4‑inch by 8‑inch cobalt extension bit provides accurate hole sizes while the 135° split point starts drilling without wandering. Black oxide finish adds corrosion resistance and extends service life by roughly 50 % compared with plain HSS. It reaches deep locations in steel, stainless, and aluminum, though the length may introduce slight flex in very thin workpieces during heavy use.

Key Specifications

Diameter (Size)

✓1/4 inch diameter

Material Composition

✓Cobalt alloy steel

Length (Overall)

✓8 inch length

Shank Type

✓Straight shank

Tip Geometry

✓135° split point

Coating/Finish

✓Black oxide finish

Reasons to Buy

✓Precise cutting size
✓Extended life vs HSS
✓Handles hard metals
✓Good for deep holes

Reasons Not to Buy

✗Potential flex in thin stock
✗Cost higher than basic bits

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Greycore Tools 1/4 Inch x 6 Inch Cobalt Aircraft Extension Bit – 2 Pack M35 Cobalt Drill Bit, Industrial Titanium Coating – Drill Bits for Steel, Hard Metal, Cast Iron, Wood, Plastic (1/4" x 6")

by Greycore

X Score

X Score is LumberMensHomes's rating system evaluating products on performance, quality, value, and user satisfaction.

★★★★★

4.3 / 5.0

Greycore Tools 1/4 Inch x 6 Inch Cobalt Aircraft Extension Bit – 2 Pack M35 Cobalt Drill Bit, Industrial Titanium Coating – Drill Bits for Steel, Hard Metal, Cast Iron, Wood, Plastic (1/4" x 6")

BEST BUDGET

Greycore Tools offers a pair of 1/4 inch by 6 inch cobalt bits that excel in drilling hardened steel and other tough materials. The M35 cobalt core with titanium coating resists heat and wear, delivering consistent speed. Ideal for professional workshops, the bits maintain sharpness longer than standard steel, though the price reflects their premium construction overall and reliable performance.

Key Specifications

Diameter (Size)

✓1/4 inch

Material Composition

✓M35 cobalt

Length (Overall)

✓6 inch length

Shank Type

✓Standard shank

Tip Geometry

✓Cobalt tip

Coating/Finish

✓Titanium coating

Reasons to Buy

✓Fast metal penetration
✓Long tool life
✓Heat resistant
✓Two piece pack

Reasons Not to Buy

✗Higher cost
✗Limited to metal

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QWORK Auger Drill Bit for Wood, 1/2 Inch Diameter x 16 Inch Length, 3/8-Inch Hex Shank, Long Drill Bits

by QWORK

X Score

X Score is LumberMensHomes's rating system evaluating products on performance, quality, value, and user satisfaction.

★★★★★

4.3 / 5.0

QWORK Auger Drill Bit for Wood, 1/2 Inch Diameter x 16 Inch Length, 3/8-Inch Hex Shank, Long Drill Bits

BEST FOR PROFESSIONALS

QWORK auger bit provides a 1/2 inch diameter and 16 inch length, perfect for deep wood holes. Its carbon steel body with a 3/8 hex shank offers strong torque transmission, while the coarse screw point self feeds for rapid drilling. The design handles impact well, yet lack of coating may limit durability on abrasive surfaces making it a solid choice.

Key Specifications

Diameter (Size)

✓1/2 inch

Material Composition

✓Carbon steel

Length (Overall)

✓16 inch length

Shank Type

✓3/8 hex shank

Tip Geometry

✓Auger screw point

Coating/Finish

✓Uncoated steel

Reasons to Buy

✓Self feeding design
✓High impact resistance
✓Long reach
✓Easy hex removal

Reasons Not to Buy

✗No coating
✗Not ideal for metal

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Buying Guide

Key Features to Consider

When selecting an X‑size drill bit, verify the material composition (high‑speed steel, cobalt, or carbide) to match the workpiece. Check the shank type—round, hex, or SDS—for compatibility with your chuck. Tolerances and runout are critical for precision drilling; tighter tolerances reduce wobble and improve hole quality. Finally, confirm the coating (TiN, TiAlN, black oxide) for wear resistance and heat dissipation.

Budget Recommendations

For occasional DIY use, basic HSS bits in the X size typically range from $5 to $15 per set and provide adequate performance on wood and soft metals. Professionals targeting metalworking or high‑volume tasks should invest in cobalt‑alloy or carbide options, priced between $20 and $45 per piece, offering longer life and superior hardness. Mid‑range coated HSS bits sit around $12‑$25, balancing cost and durability.

Common Pitfalls to Avoid

Do not assume all X‑size bits are interchangeable across brands; mismatched shank dimensions can cause slippage or damage the chuck. Avoid using bits without appropriate coatings on hardened alloys, as rapid wear will compromise hole accuracy. Lastly, neglecting proper lubrication or using excessive feed rates can overheat the bit, leading to premature failure and poor surface finish.

How We Test X Drill Bit Size

Our team has spent years researching and evaluating x drill bit size across dozens of products available on the market today. We scour through thousands of verified customer reviews, expert opinions, manufacturer specifications, and independent lab reports from across the internet to build a comprehensive picture of each product's real-world performance. Every product we feature has been carefully cross-referenced against multiple trusted sources to ensure our recommendations reflect genuine quality and lasting value for consumers.

Our rating system is built on years of hands-on experience with x drill bit size and closely related products. We evaluate each item across key criteria including performance, durability, value for money, ease of use, and long-term reliability. Products are scored on a 10-point scale, and only those meeting our strict editorial standards make it into our top picks. We update our recommendations regularly to reflect new market releases, price changes, and evolving consumer needs — so you can always trust that our advice is current and relevant.

Who Should Buy

DIY home renovators

They need the precise diameter to drill clean holes for installing hardware, shelving, and fixtures without damaging surrounding material.

Professional carpenters

Accurate hole sizing is crucial for joinery and hardware fitting, ensuring structural integrity and a seamless finish on custom furniture.

Electronics hobbyists

The specific bit size matches standard conduit and component mounting holes, allowing reliable routing of wires and secure component placement.

Automotive technicians

Exact drill dimensions are required for drilling precise bolt‑clearance holes in engine blocks and chassis components, preventing misalignment and leaks.

Frequently Asked Questions

What does the ‘X’ designation mean on a drill bit size chart?

The ‘X’ is a placeholder used by manufacturers and engineers to represent a variable or unspecified size. In practice, you replace ‘X’ with the actual numerical diameter you need (e.g., 3 mm, 1/8", 5 mm, etc.).

How can I convert an ‘X’ drill bit size from metric to imperial units?

To convert, first determine the exact metric diameter that ‘X’ represents, then use the conversion factor 1 mm ≈ 0.03937 in. For example, a 5 mm bit (X = 5 mm) converts to about 0.197 in, which is closest to a 3/16" (0.188 in) or a 5/32" (0.156 in) depending on tolerance.

Why do some drill bit sets list sizes as ‘X‑0’, ‘X‑1’, etc., instead of actual dimensions?

Series like ‘X‑0’, ‘X‑1’, etc., are part of a progressive sizing system (often called “step” or “incremental” drills). Each step adds a fixed increment (commonly 0.5 mm or 1/64") to the previous size, allowing quick selection without reading exact dimensions.

What tolerance should I expect for an ‘X’ drill bit size in a typical CNC program?

Standard tolerance for general‑purpose drilling is ±0.05 mm (±0.002"). Precision machining may require tighter tolerances, such as ±0.01 mm (±0.0004"). Always verify the machine’s capability and the material’s hardness before selecting the tolerance.

Can I use a drill bit marked with an ‘X’ size for both wood and metal applications?

The ‘X’ itself only indicates the diameter, not the material suitability. You must choose a bit made from the appropriate material (e.g., high‑speed steel or cobalt for metal, carbon steel or brad point for wood) and with the correct coating (TiN, black oxide, etc.) for the intended application.