Which Drill Bit Is 8mm? A Practical Guide from Drill Bits Pro

What is an 8 mm drill bit?

If you are asking which drill bit is 8mm, the answer is straightforward: it is a metric drill bit with a cutting diameter of eight millimeters. In practice you will find 8 mm bits labeled on the shank or near the point of the bit. The most common form is a twist bit made from high speed steel (HSS), sometimes carbide-tipped for longer life in tougher materials. The 8 mm size is popular because it accommodates standard fasteners such as M6 and M8 applications, pilot holes for larger hardware, or clearance holes in assemblies. Because tolerances vary by material and manufacturing, you should always measure the drill bit with calipers if precision is critical. For DIY projects you’ll often use 8 mm to create holes for dowels, bolts, or cables. In metalworking, 8 mm may be used for creating clean clearance holes or for preparing a tapped hole layout. The key is to choose a bit type that matches the material and the finish you need.

Common 8 mm bit types

There are several 8 mm bit types commonly found in hardware stores and on job sites. The most familiar is the metric twist bit, available in high speed steel (HSS) for wood and many plastics, and carbide-tipped variants for metal or harder composites. For concrete and masonry, masonry bits with a 8 mm diameter are available, often with a tungsten carbide tip. Step bits sometimes come in 8 mm increments and can be used to create a hole that ends at or near eight millimeters, though this is more common for rounded or enlarging holes in sheet metal or plastic. For specialty work, cobalt or carbide bits offer improved wear resistance when drilling tough alloys. When selecting, rely on the material you’ll work with and the finish you want to achieve.

Material and coating considerations

Material and coating choices directly affect performance and longevity. For soft materials such as pine or plastic, an HSS twist bit is typically sufficient and economical. For metals, especially aluminum and steel, look for high speed steel bits with a coating like titanium nitride or a carbide-tipped variant for longer life and smoother cutting. In very hard or abrasive materials, consider a cobalt alloy or solid carbide option if the bit geometry supports it. Coat types reduce wear, but never substitute for choosing the correct bit material for the job. If you’re drilling in masonry or concrete, always opt for a dedicated masonry bit with a tungsten carbide tip and a robust shank to withstand hammer action.

Matching bit to material: wood, metal, plastic

Woodworks: use a sharp 8 mm twist bit in high speed steel for clean, fast holes; predrill a pilot hole if necessary to prevent splitting. Metalwork: for steel and aluminum, choose an HSS or carbide-tipped bit; use lubricant for metal to reduce heat. Plastic: select a sharp bit with a clean edge to reduce wander and melt risk. In all cases, ensure the bit is sharp, the workpiece is clamped, and the drill is aligned square to the surface. For larger projects, consider step bits or pilot-hole strategies to manage entry and avoid wandering.

Sizing, verification, and avoiding common mistakes

Always verify that your bit size is truly 8 mm before drilling, especially if you are replacing a worn bit. Use calipers or a micrometer to check the diameter and compare against the packaging markings. When drilling, start with a light touch to establish a true center and prevent wandering. Maintain steady pressure and avoid forcing the bit through the material, which can dull the edge or bend the bit. If the hole needs precise depth, use a drill stop or a piece of tape to mark depth. Remember that tolerances vary by material and tool quality, so plan for a little adjustment if a perfect 8 mm hole is required.

Techniques for accurate 8 mm holes

Accurate 8 mm holes start with proper setup. Clamp the workpiece securely and use a center punch or pilot hole in metal to guide the bit. In wood, start with a small pilot hole to prevent splitting and then drill the final diameter. Maintain perpendicular alignment to the surface and feed the drill smoothly. When drilling metal, use cutting lubricant if possible and back off if the bit binds. For plastic, avoid overheating by using slower feed and short cycles. Match your RPM to the material; higher speeds are not always better, especially on harder substrates. With practice, you’ll minimize tear-out and achieve cleaner edges.

Maintenance and care for an 8 mm drill bit

Keep an 8 mm drill bit sharp by periodic honing or professional re-sharpening if you use metal- or carbide-tipped variants. Clean the flute grooves to remove chips, and wipe down bits after use to prevent corrosion. Store bits in a dry, organized rack and avoid bending or dropping the shank. Use a proper bit holder to prevent dulling the tip, especially if the bit contacts hard materials or a non-flat surface. If you notice wandering or rough cutting, assess the bit for dullness, misalignment, or incorrect material pairing, and replace or re-sharpen as needed.

Quick-start checklist for 8 mm drilling

• Confirm the material and select the correct 8 mm bit type
• Clamp the workpiece securely and mark the hole location
• If metal, consider a pilot hole and lubricant
• Drill slowly and steadily, checking alignment frequently
• Verify the hole diameter with calipers after drilling
• Clean and store the bit properly after use