A 135 Split Point Cobalt Letter Drill Bits is one of the most useful tools in my set. It cuts fast, stays sharp, and doesn’t slip on smooth metal. The flat tip helps it grab the surface right away, and the cobalt keeps it strong even when it gets hot.
In this guide, I’ll explain what this drill bit is, why it works so well, and when I use it. I’ll also cover sizes, tips for better drilling, and how to make the bit last longer.
Article Summary
- What Is a 135° Split Point Cobalt Letter Drill Bit?
- Why I Choose 135° Split Point Bits
- Understanding Letter Drill Bit Sizes
- When to Use a Cobalt Drill Bit
- How I Use 135° Split Point Bits the Right Way
- Benefits of Using These Drill Bits
- Common Projects I Use Them For
- My Favorite Brands for 135° Split Point Cobalt Bits
- Letter Drill Bits vs. Number and Fractional Bits
- How to Sharpen a Cobalt Drill Bit
- What Makes the 135° Split Point So Special?
- Cobalt vs. Titanium Drill Bits: Which Is Better?
- How I Store My Letter Drill Bits
- Tips to Make Your Drill Bits Last Longer
- FAQ: A 135 Split Point Cobalt Letter Drill Bits
- Conclusion: Why I Stick With 135° Cobalt Letter Bits
What Is a 135° Split Point Cobalt Letter Drill Bit?
Let’s break that long name into parts:
- 135° Split Point: This is the angle at the tip of the bit. A 135-degree angle is flatter than the common 118-degree tip. It helps the bit start cutting right away without sliding or “walking” on the surface.
- Split Point: The tip is split, not just sharp. This design centers the bit, so you don’t need a punch to start your hole. It also reduces pressure, making drilling easier.
- Cobalt: These bits are made with cobalt steel, usually 5% to 8%. Cobalt makes the bit harder and heat-resistant. That’s great for drilling tough materials like stainless steel or cast iron.
- Letter Drill Bit: Instead of using number or fractional sizes, these bits are sized using letters from A to Z. Each letter stands for a specific size. For example, a size “F” bit is 0.257 inches.
Why I Choose 135° Split Point Bits
1. No Walking on Metal
Before using split point tips, my bits often wandered on smooth surfaces. That meant crooked holes or scratched metal. With a 135° split point, the tip stays put. I can start drilling right away—no need to punch a center mark first.
2. Faster and Smoother Starts
These bits don’t need much pressure. I just press gently, and the bit grabs the material. That saves energy and reduces strain on my hands and drill motor.
3. Clean Holes Every Time
Whether I’m drilling aluminum, brass, or stainless steel, the holes come out clean and round. That’s because the flatter tip cuts evenly and doesn’t tear the material.
4. Great for Hard Metals
Cobalt helps the bit stay sharp longer. I’ve used the same cobalt bit on stainless steel many times without sharpening. It gets hot, but it keeps cutting.
Understanding Letter Drill Bit Sizes
Letter bits range from A to Z. Here’s a quick view of a few sizes:
| Letter | Size (Inches) | Size (mm) |
|---|---|---|
| A | 0.234 | 5.94 |
| D | 0.246 | 6.25 |
| F | 0.257 | 6.53 |
| H | 0.266 | 6.76 |
| K | 0.281 | 7.14 |
| M | 0.295 | 7.49 |
| Z | 0.413 | 10.49 |
These are helpful when a fractional or numbered bit doesn’t fit. I use them a lot when working with bushings, bearings, or reamers.
When to Use a Cobalt Drill Bit
I switch to cobalt bits in three cases:
- Drilling Hardened Metals – Steel, stainless, and titanium don’t stand a chance.
- High Heat Situations – Long drilling sessions build up heat. Cobalt handles that better.
- Precision Work – The split point keeps things centered and sharp.
How I Use 135° Split Point Bits the Right Way
1. Go Slow on Speed
Cobalt bits aren’t about speed. I use slower drill RPMs, especially on steel. Too much speed makes them dull fast.
2. Use Cutting Oil
A few drops of oil can go a long way. It keeps the bit cool and cuts smoother.
3. Keep It Straight
I always keep the drill perpendicular to the surface. That way, the tip grabs evenly and doesn’t chip.
Benefits of Using These Drill Bits
- ✅ Less Pressure Needed – Easier on your arms and tools.
- ✅ Stays Centered – Perfect for drilling by hand.
- ✅ Lasts Longer – Cobalt resists wear and heat.
- ✅ No Pre-Drilling Needed – Starts right where I want it.
Common Projects I Use Them For
- Car repairs
- Electrical boxes
- Stainless sink installations
- Metal brackets
- Bolt holes in steel beams
My Favorite Brands for 135° Split Point Cobalt Bits
After years of trial and error, these are my go-to brands:
- Norseman – Tough and reliable.
- Chicago-Latrobe – Great for pros and shops.
- Drill America – Affordable with good performance.
- Irwin – Good value for basic jobs.
Letter Drill Bits vs. Number and Fractional Bits
Here’s why I sometimes prefer letter bits:
- Unique Sizes – Some holes are in-between normal sizes.
- Better Fit for Fasteners – Letter sizes often match thread tap sizes.
- Added Precision – Great when tolerance matters.
How to Sharpen a Cobalt Drill Bit
Even cobalt bits get dull. When that happens, I sharpen them using a bench grinder or drill bit sharpener. The key is keeping the 135° angle. A little care goes a long way to bring them back to life.
What Makes the 135° Split Point So Special?
I get this question a lot. Here’s the simple answer: it cuts fast and straight.
Compared to the standard 118°, the 135° split point:
- Starts without walking
- Needs less force
- Keeps its edge longer
- Doesn’t clog as easily
It’s especially helpful when I don’t have a drill press and need to work by hand.
Cobalt vs. Titanium Drill Bits: Which Is Better?
Both have their place. But here’s my take:
| Feature | Cobalt | Titanium Coated |
|---|---|---|
| Material | Solid cobalt steel | High-speed steel w/ coat |
| Best For | Hard metals | Soft to medium metals |
| Re-sharpenable | Yes | No (coating wears off) |
| Heat Resistance | Excellent | Good |
| Price | Higher | Lower |
If I’m drilling steel, I grab cobalt every time. For plastic or soft aluminum, titanium-coated bits are fine.
How I Store My Letter Drill Bits
I use a labeled metal index case. That way, I can find the size I need fast. I also keep them clean and dry to avoid rust.
Tip: If you’re buying a full set, get one with the letters clearly etched on each bit. It saves guessing later.
Tips to Make Your Drill Bits Last Longer
- Go slow with harder materials.
- Use oil to cool and lube.
- Don’t push too hard—let the bit do the work.
- Clean after each use.
- Sharpen when needed.
FAQ: A 135 Split Point Cobalt Letter Drill Bits
1. What is a 135° split point drill bit used for?
It’s great for drilling metal. The tip stays centered and cuts fast without wandering.
2. Can I use cobalt bits on wood or plastic?
Yes, but it’s overkill. These bits shine on tough metals, not soft stuff
3. Are letter drill bits better than fractional?
Not better, just different. They fill in the gaps where fractional sizes don’t fit.
4. How do I know if my drill bit is cobalt?
Cobalt bits are often darker, more rigid, and usually marked M35 or M42. They feel heavy and cut tough stuff with ease.
5. How long do cobalt drill bits last?
With care, they last a long time—especially if you drill slowly, use oil, and keep them sharp.
Conclusion: Why I Stick With 135° Cobalt Letter Bits
For me, these bits are a no-brainer. They save time, cut better, and hold up job after job. Whether you’re a pro or a DIYer like me, having a good set of 135° split point cobalt letter drill bits in your toolbox is a smart move.