Letter Drill Bit Set for Metal Fabrication Projects

By Drill Hog® | Published: 2026-10-22

Category: How-to Guides

Learn how to choose and use a letter drill bit set for metal fabrication, with step-by-step guidance and common mistakes to avoid.

Quick answer

For metal fabrication, a letter drill bit set like the Drill Hog 26 Pc COBALT M42 set covers A to Z sizes, providing the precision and durability needed for clean holes in tough materials.

Why letter sizes matter in metal fabrication

Letter drill bits fill the gaps between fractional and number sizes, giving you exact hole diameters for tasks like tapping threads or matching a specific fastener. In metal fabrication, where tolerances are tight, using a letter size can mean the difference between a perfect fit and a rework.

A full A-Z set ensures you have the right size on hand without hunting for a single bit. This saves time and keeps projects moving, especially when you're working on a job that requires multiple hole sizes.

Cobalt M42 vs. standard HSS

Cobalt M42 steel contains additional cobalt and molybdenum, which gives it higher heat resistance and hardness compared to standard high-speed steel. This makes it ideal for drilling into harder metals like stainless steel and cast iron without losing its edge quickly.

For metal fabrication, where you might be drilling several holes in a row, the heat resistance of cobalt bits helps maintain cutting performance and extends bit life. It's a trade-off: cobalt bits cost more upfront, but they reduce the need for frequent replacements.

How to use a letter drill bit set for metal fabrication

Select the right letter size: Determine the exact hole diameter needed for your project, whether for tapping, fastening, or alignment. Use a drill bit size chart to match the letter to the required fractional or metric size. Check the chart twice before drilling to avoid costly mistakes.
Secure the workpiece: Clamp the metal piece firmly to a workbench or use a vise to prevent movement. This ensures accuracy and reduces the risk of bit breakage. Never hold metal by hand while drilling; always secure it.
Use cutting fluid: Apply a suitable cutting fluid or lubricant to the drilling area to reduce heat and friction. This prolongs bit life and improves hole quality. Keep a bottle of cutting fluid nearby and reapply as needed.
Start with a pilot hole: For larger letter sizes, drill a smaller pilot hole first. This guides the bit and reduces the force needed, preventing wander and premature wear. Pilot holes are especially important when drilling into hard metals.
Drill at the correct speed: Use a slower spindle speed for larger diameters and harder materials. High speeds can overheat the bit and cause it to dull quickly. Refer to the drill manufacturer's speed chart for the specific material and bit size.
Clear chips regularly: Retract the bit periodically to break and clear chips. This prevents clogging and reduces heat buildup, especially in deep holes. If you see long stringy chips, you're drilling too fast or not clearing often enough.

Product spotlight

26 Pc LETTER Drill Bit Set A-Z Bits COBALT M42 Drilll Stand Drill Hog USA: Drill Hog 26 Pc COBALT M42 Letter Drill Bit Set includes sizes A to Z, with diameters ranging from 0.234 inches (A) to 0.412 inches (Z). Having the complete A-Z range means you can handle any letter-size hole requirement without buying individual bits, saving time and ensuring you're never stuck without the right size.
26 Pc LETTER Drill Bit Set A-Z Bits COBALT M42 Drilll Stand Drill Hog USA