How to Choose the Right Drill Bit for Metal
By Drill Hog® | Published: 2026-10-28
Category: Buying Guides
Learn how to select the best metal drill bits for your project, including cobalt M42, step, and left-hand bits, with clear decision rules and trade-offs.
Quick answer
Choose cobalt M42 drill bits for hard metals, step bits for thin sheet metal, and left-hand bits for extracting broken fasteners.
Metal type dictates bit material
For drilling into hardened steel, stainless steel, or cast iron, a cobalt M42 bit is essential. Cobalt M42 steel has a high melting point and retains hardness at high temperatures, preventing bit wear. For softer metals like aluminum or brass, standard high-speed steel bits work, but cobalt M42 lasts longer even there.
Step bits vs. twist bits for thin metal
Step drill bits are ideal for thin sheet metal because they create clean, burr-free holes without catching. A step bit's conical design lets you drill multiple hole sizes with one bit. Twist bits can grab and walk on thin metal, but a 135-degree split point helps prevent that.
Left-hand bits for broken fastener removal
When a screw or bolt snaps off, a left-hand drill bit rotates counterclockwise to bite into the broken piece. Combined with a screw extractor, it can back out the fastener without damaging the surrounding material. This set is specialized and not for general drilling.
Decision rules for choosing a metal drill bit
- Hard metal (steel, stainless, cast iron): Choose a cobalt M42 twist bit. The cobalt alloy maintains cutting edge hardness at high drilling temperatures. Check that the bit has a 135-degree split point to reduce walking on hard surfaces.
- Thin sheet metal (up to 1/8"): Use a step drill bit. The stepped design prevents grabbing and produces a clean hole without deburring. Select a set with multiple step ranges to cover common hole sizes like 1/8" to 1/2".
- Broken fastener removal: Pick a left-hand drill bit set with matching spiral screw extractors. Drill into the broken fastener with the left-hand bit, then use the extractor to back it out. Start with a small pilot hole to avoid enlarging the broken piece too much.
Product facts
- Drill Hog® Super Premium Cobalt M42 Quad Flute Step Drill Bit Set: Includes two step bits: one with 6 steps (3/16" to 1/2") and one with 13 steps (1/8" to 1/2"), both with quad spiral flute design. The quad spiral flute clears chips faster, reducing heat buildup and extending bit life in sheet metal.
Drill Hog® Super Premium Cobalt M42 Quad Flute Step Drill Bit Set - Drill Hog® 10 Piece Cobalt M42 Left Hand Drill Bit Set: Set contains 5 left-hand cobalt M42 drill bits and 5 spiral screw extractors for removing broken fasteners. You get matched bits and extractors in one kit, so you don't have to guess which extractor fits the drilled hole.
Drill Hog® 10 Piece Cobalt M42 Left Hand Drill Bit Set
Who should buy what
Best for
- DIYers and pros drilling into hardened steel or stainless steel regularly
- Anyone needing clean holes in thin sheet metal for electrical or HVAC work
- Mechanics and technicians who remove broken bolts and screws
Not for
- Drilling wood or plastic—cobalt M42 bits are overkill for soft materials
- High-volume production drilling in thick steel plate—consider carbide-tipped bits instead
