Identifying Your Twist Drill Bit

Choosing the right twist drill bit is only half the battle; using it at the right speed is what makes the work easy and keeps your tools sharp. This QLT Insight identifies what drill bit you have and how to use it.

Part 1: Colour Identification

The colour of a drill bit usually indicates its coating or material composition.

The "Point" Check

Always check the tip shape regardless of colour:

• V-Shaped Tip: Metal and General Purpose.
  
  
• Needle Centre Point: Wood Only (Brad Point).
  
  
• Shovel/T-Shape Tip: Masonry (Brick/Concrete).

Part 2: Speed Chart (RPM)

The Golden Rule: The harder the material and the larger the drill bit, the slower you should spin it.

Part 3: The Shank

The shank is the part that goes into the drill. Not all shanks fit all drills.

• Straight (Round): The most common. Best for standard drill chucks. It can slip if you’re drilling through heavy metal, but it’s the most versatile.
  
  
• Hex (6-sided): Designed for impact drivers and quick-change chucks. These never slip, making them great for high-torque tasks like driving screws or drilling into thick wood.
  
  
• SDS (Slotted): These have distinct grooves. They are for Heavy Duty Rotary Hammers (masonry drills) only. They won't work in your standard drill without a special adapter.

Part 4: The Point Angle

If you look at the bit from the side, the angle of the tip tells you about the material it's meant to "bite" into.

• 118° (Standard Point): This is a sharper, steeper point. It’s the "aggressive" angle designed for softer materials like wood, plastic, and mild steel. It's easier to start by hand but wears out faster in hard metal.
  
  
• 130° / 135° (Split Point): This is a flatter tip. It’s designed for harder metals (like stainless steel). It has more surface area in contact with the metal, which helps it cut instead of just spinning and heating up.

Search Tip: Many high-quality 135° drill bits are "self-centring," meaning they won't "walk" across the metal when you start

Part 5: Length of Jobber/Stub

The length of the bit isn't just about how deep the hole is; it’s about stiffness.

• Jobber Length: This is the "standard" length you see in every hardware store set. Great for general work.
  
  
• Stub (Mechanic's) Length: These are much shorter. Why use them? Because they are stiffer. If you are drilling into very hard metal, a long "jobber" bit can flex and snap. A stub bit stays rigid and puts all the force into the tip.

Pro-Tips for Success

How to Gauge Speed by Eye

Most handheld drills don't have a tachometer. Use these visual cues:

• For Metal: You should see the bit spinning. If it’s a total blur, you’re likely going too fast. You want to see "chips" (curls of metal) coming out, not fine dust.
  
  
• For Wood: A faster speed is usually better to prevent "tear-out" and splintering, but if the wood starts to smell like it’s burning, back off the speed.

When to Use Oil

If you are drilling into any metal other than aluminium or cast iron, use a drop of cutting fluid or multi-purpose oil. This lubricates the flutes and prevents the bit from "work-hardening" the metal, which makes it impossible to finish the hole.

Final Verdict

If you are a homeowner building a kit, buy a Rolled (HSS-R) Black Oxide set for your everyday needs. If you have a specific project involving stainless steel or precision machinery, skip the cheap stuff and invest in a single Ground (HSS-G) Cobalt bit for that specific hole. Your drill (and your sanity) will thank you! Find ALL Jobber Twist Drill Bits & Sets From QLT Supplies here.