10 Quick Tips in Selecting the Right Drill Bit:
- Material Type: Choose bits designed for wood, metal, plastic, or masonry.
- Drill Bit Gauge: Use a gauge to identify bit sizes quickly.
- Screw Match: Match the bit to the screw's shank diameter.
- Size Charts: Cross-reference metric and imperial sizes.
- Test First: Test on scrap material before the final piece.
- Bit Labels: Ensure bits are clearly labeled for easy identification.
- Pilot Holes: Use smaller bits for pilot holes to prevent splitting.
- Speed Settings: Adjust drill speed based on bit size and material.
- Bit Quality: Invest in high-quality bits for better performance.
- Storage: Keep bits organized in a labeled case or holder.
Why Drill Bit Sizes Matter
Picking the right drill bit size ensures your screws and bolts fit perfectly, preventing damage to your workpiece and the drill bit.
Metric vs. Imperial: The Basics
Metric sizes are in millimeters, while imperial sizes are in inches. For example, a 10mm drill bit is roughly the same as a 3/8 inch bit. Knowing these conversions can save you a lot of frustration, especially when working with imported tools and materials.
Must-Have Bit Sets for Your Toolbox
Whether your are just starting or replenishing, these are our must-have sets to consider:
- Metric Drill Bit Set
- Imperial Drill Bit Set
- Countersink Bits
- Panel Drill Bit sets
- Sutton Tools Long Series Drill Bits
These sets can cover all your initial drilling needs, ensuring you always have the right tool for the job.
CLICK TO DOWNLOAD OUR FREE PRINTABLE DRILL BIT SIZE CHART
PRO TIP: You can also buy a Sutton M8100650 Metric and Imperial Multi Function Gauge to measure your drill bits, fasteners, nuts and threads.
Extra FREE CHARTS below:
- Anchor Bolt Size Chart: Find metric anchor bolts like countersunk head, drop-in, hex flange nut, flush head, and stud anchors. Common diameters included.
- Fastener Reference Chart: Cross-reference bolt, nut, or screw sizes with metric, Unified Thread Standard, and British Thread Standards. Simple illustrations included.
- Loctite Application Chart: Choose the right Loctite product for various materials and surfaces.
- Pulley Size Chart: Browse aluminum and cast-iron pulleys for different belt sections and grooves. Metric and imperial sizes available.
- Socket Sizing Cross-Reference Chart (Metric-Imperial Values): Match sockets and drives in metric and imperial sizes.
- Spanner Size Chart: Find the right spanner size for hexagonal bolts, nuts, or screws. Metric and imperial sizes included.
- Tapping Drill Size Chart for Thread Cutting Taps: Identify the right drill size for pilot holes before cutting threads. Metric and imperial sizes included.
No matter the project, choosing the correct drill bit size is crucial for achieving cleaner, more precise holes. Not only does it enhance the quality of your work, but it also extends the life of your tools and materials. By investing a little time in selecting the right bit, you can ensure professional results and avoid unnecessary wear and tear.
Browse the AIMS Carbide Drill Bits range — solid carbide and tungsten carbide tipped, in metric and imperial sizes.
People Also Ask — Choosing Drill Bits
Q: What drill bit should I use for stainless steel?
Stainless steel requires a drill bit with high heat resistance and edge toughness. Cobalt drill bits (HSS-Co, typically 5% or 8% cobalt) are the standard choice — the cobalt content raises the bit's resistance to the work-hardening effect that stainless produces under heat and friction. Use cutting fluid, reduce spindle speed compared to mild steel by 30–50%, and use moderate feed pressure to prevent the work-hardening effect. Solid carbide drills provide the highest performance in stainless in production environments but require a rigid, vibration-free setup.
Q: What is the difference between HSS and carbide drill bits?
High-speed steel (HSS) drill bits are tough, less brittle, and tolerant of slight misalignment — suitable for general workshop use on steel, aluminium, and plastics. Carbide drill bits (solid carbide or carbide-tipped) are significantly harder than HSS, hold their cutting edge longer, and can run at higher speeds — but they are brittle and require a rigid machine setup with minimal runout. HSS is typically the right choice for hand drills and flexible setups; carbide is the right choice for CNC machining centres, vertical mills, and dedicated drilling machines where rigidity is assured.
Q: How do I select the right drill bit size for a tapped hole?
The correct tap drill size depends on the thread standard and the required percentage of thread engagement. For metric coarse threads, a common rule is: tap drill diameter (mm) = nominal diameter (mm) − pitch (mm). For example, M8 × 1.25 → 8 − 1.25 = 6.75mm tap drill (often rounded to 6.8mm for 75% thread engagement). Use the tap drill size charts in the AIMS threading guide for precise recommendations across metric coarse, metric fine, UNC, UNF, and BSP thread series.
Q: Why do my drill bits keep breaking when I drill metal?
Drill bit breakage in metal most commonly results from: (1) excessive feed pressure — forcing the bit rather than letting the cutting edges do the work; (2) running at too-high a speed for the material — raises heat, softens the cutting edge; (3) running at too-low a speed — reduces chip evacuation, increases torque on the bit; (4) inadequate cutting fluid — causes overheating and welding of chips to the cutting edge; (5) a dull bit — a sharp drill requires far less force and runs cooler. Always use cutting fluid on steel and stainless, and check your speed and feed against the recommended values for the bit diameter and material.
Q: What drill bit is best for drilling into concrete or masonry?
Masonry drill bits have a carbide-tipped cutting edge brazed to a steel shank, designed for use in a hammer drill or SDS rotary hammer. The percussion action of the drill fractures the aggregate while the carbide tip clears the dust. For SDS drills, use SDS-Plus or SDS-Max bits matched to the drill's chuck type. Do not use standard HSS drill bits on concrete or masonry — they will blunt immediately. For very hard stone or reinforced concrete, diamond-tipped core drills may be required for large diameter holes.
AIMS Industrial stocks long drill bits — see the full range for trade and industrial use.