Technical Foundation
What Is a Drill Bit?
Drill bit selection starts with the material being cut: high-speed steel (HSS) bits handle general-purpose drilling in mild steel, wood and plastic; cobalt bits (typically M35 or M42, containing 5-8% cobalt) resist the heat generated in stainless steel and hardened alloys; and solid carbide bits hold an edge in abrasive materials and high-volume production but are more brittle and less tolerant of flex or misalignment than HSS. Point angle also matters — a 118-degree point suits general-purpose drilling in softer materials, while a 135-degree split point centers faster and resists walking in hard or curved surfaces.
Shank type determines what the bit can be chucked into: straight round shanks fit standard drill chucks, while reduced (3-flat or hex) shanks let a large-diameter bit run in a smaller chuck or allow positive drive in impact drivers. Flute design and helix angle affect chip evacuation — slow-helix bits suit brass and plastics prone to grabbing, while standard-helix bits balance chip clearing and cutting speed across most general-purpose work.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Material | HSS, cobalt (M35/M42), solid carbide | Determines heat resistance and suitability for stainless, cast iron, or abrasive materials |
| Point Angle | 118° standard, 135° split point | Split point self-centers and resists walking on hard or curved surfaces |
| Diameter System | Fractional, wire gauge, letter, metric | Tap drill charts and print callouts specify one system — mismatched systems cause oversize or undersize holes |
| Shank Type | Straight round, 3-flat, hex reduced shank | Reduced shanks let large bits run in smaller chucks or drive positively in impact tools |
| Coating | Black oxide, TiN, TiAlN, bright/uncoated | Coatings reduce friction and heat buildup, extending tool life in harder or abrasive materials |
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Applications
Where Drill Bits Get Used
Drill bits are specified by the material being cut, the required hole diameter, and the chuck or holder the equipment uses.
General Fabrication & Machine Shops
Jobber-length HSS and cobalt bits for routine hole drilling in mild steel, aluminum, and stainless components.
Sheet Metal & HVAC Ductwork
Step drill bits producing multiple clean hole diameters in thin sheet without deburring or bit changes.
Electrical & Panel Work
Reduced-shank and cobalt bits for drilling enclosure panels, conduit knockouts, and mounting holes.
Construction & Masonry
Carbide-tipped masonry bits for anchor holes in concrete, block, and brick.
Production Machining
Solid carbide bits on CNC equipment for high-volume, tight-tolerance hole drilling in aluminum and cast iron.
MRO & Facilities Maintenance
General-purpose bit sets stocked for field repair and equipment modification drilling across mixed materials.
FAQ
Drill Bits Questions, Answered
What's the difference between HSS and cobalt drill bits?
HSS (high-speed steel) bits are general-purpose and cost-effective for wood, plastic, and mild steel. Cobalt bits (usually M35 or M42 alloy, containing 5-8% cobalt) retain hardness at higher temperatures, making them better suited to stainless steel, tool steel, and other hard or abrasive materials where HSS bits would dull quickly from heat buildup.
When should I use a solid carbide drill bit instead of cobalt?
Solid carbide bits hold a sharp edge far longer than cobalt in abrasive materials and high-volume production runs, and they run at higher speeds. However, carbide is more brittle than cobalt or HSS — it doesn't tolerate flex, misalignment, or interrupted cuts well, so it's best suited to rigid CNC setups rather than hand-held drilling where the bit may wander or bind.
What does the drill point angle mean, and does it matter?
Point angle is the angle ground into the bit's cutting tip — 118 degrees is the traditional general-purpose angle, while 135-degree split-point bits have a self-centering geometry that resists walking on hard, curved, or slippery surfaces and starts cutting with less pressure. For drilling hardened materials or off-angle surfaces, a 135-degree split point is usually the better choice.
How do fractional, wire gauge, letter, and metric drill sizes relate to each other?
These are four separate numbering systems for bit diameter. Fractional sizes (1/16", 1/4", etc.) are common imperial sizes; wire gauge sizes (numbered 1-80, smaller number = larger bit) and letter sizes (A-Z) fill in diameters between fractional sizes, often used for tap drill and clearance hole charts; metric sizes are specified directly in millimeters. A tap drill chart or print callout will specify which system applies — mixing them up produces the wrong hole size.
Why do some drill bits have a reduced or 3-flat shank instead of a straight round shank?
A reduced shank has a shank diameter smaller than the bit's cutting diameter, letting a large bit be chucked into a smaller drill or impact driver. A 3-flat (or hex) shank adds flat faces the chuck jaws can grip positively, preventing slippage under the torque spikes an impact driver produces — straight round shanks can spin in the chuck under that kind of torque.
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