Beginner's Guide to Annular Cutters: Material Selection, Sizing & Pilot Pin Compatibility

Beginner's Guide to Annular Cutters: Material Selection, Sizing & Pilot Pin Compatibility

What Is an Annular Cutter — and Why Use One?

If you've ever drilled a large hole through steel with a standard twist drill, you know the struggle: slow cutting, excessive heat, and a lot of wasted material. Annular cutters (also called hole cutters or mag drill bits) solve all of that.

Unlike a twist drill that removes the entire plug of material as chips, an annular cutter only cuts the outer ring of the hole — leaving a solid slug that simply falls out when the cut is complete. The result is:

  • Faster cutting — less material removed means less work
  • Cooler operation — reduced friction extends tool life
  • Cleaner holes — no pilot hole required, and the finish is precise
  • Less power required — ideal for portable magnetic drills

Whether you're in metal fabrication, HVAC, structural steel, or automotive work, annular cutters are a game-changer for drilling clean, accurate holes in metal.

Step 1: Choose Your Material — HSS vs. Carbide Tipped

The single most important factor in selecting an annular cutter is the material it's made from. There are two main options:

High-Speed Steel (HSS)

HSS annular cutters are the workhorse of the industry. They're versatile, cost-effective, and well-suited for most everyday drilling applications.

Best for:

  • Mild steel, structural steel, and iron
  • General fabrication and construction
  • Occasional or moderate-use applications
  • Shops looking for a reliable, budget-friendly option

Our Nitto Kohki HSS Annular Cutters are a top choice for general-purpose work, ranging from $32–$93 depending on size. Nitto Kohki is one of the most trusted names in the industry, and their HSS cutters deliver consistent performance across a wide range of applications.

Carbide Tipped

Carbide-tipped annular cutters take things to the next level. The carbide inserts on the cutting edges are significantly harder than HSS, which means they stay sharp longer and can handle tougher materials.

Best for:

  • Hardened steel, stainless steel, and abrasive alloys
  • High-volume production environments
  • Applications where tool longevity is critical
  • Situations where frequent cutter changes slow you down

Our Nitto Kohki Jetbroach Carbide Tipped Annular Cutters ($65–$130) are engineered for demanding applications. The carbide tips maintain their edge far longer than HSS, making them a smart investment for high-use shops even at a higher upfront cost.

Quick Rule of Thumb: If you're drilling mild steel occasionally, go HSS. If you're drilling stainless, hardened steel, or running high volumes, go carbide.

Step 2: Select the Right Size

Annular cutters are defined by two key dimensions:

Diameter

This is the size of the hole you want to cut. Annular cutters are available in a wide range of diameters — typically from 9/16" up to 3" or more. Always match the cutter diameter to your required hole size. Unlike twist drills, annular cutters don't require stepping up through multiple sizes.

Cutting Depth (Depth of Cut)

This refers to how deep the cutter can cut in a single pass. Common depths are 1", 2", and 3". Make sure the cutter's depth of cut exceeds the thickness of the material you're drilling through. For example, if you're drilling through 1.5" steel plate, you need a cutter with at least a 2" depth of cut.

Pro Tip: When in doubt, go slightly larger on depth. A cutter that's too shallow for your material won't complete the hole — and you'll have to start over.

Step 3: Understand Pilot Pin Compatibility

Most annular cutters use a pilot pin — a spring-loaded center pin that sits inside the cutter and helps you locate the center of your hole before cutting begins. When the cutter contacts the material, the pilot pin retracts and the cutting begins.

Pilot pins are not universal. They must match:

  • The cutter's shank size — most mag drill cutters use a 3/4" Weldon shank, but always verify
  • The arbor/chuck on your magnetic drill — the pilot pin must fit the arbor's center bore

Using the wrong pilot pin can result in poor hole location, cutter damage, or unsafe operation. Browse our Pilot Pins collection to find the right match for your cutter and drill setup.

Note: Some applications — particularly when using a drill press or milling machine rather than a mag drill — may not require a pilot pin. Check your equipment's requirements before purchasing.

Real-World Application Examples

Still not sure which cutter is right for you? Here's how different industries typically use annular cutters:

  • Metal Fabrication: HSS cutters for structural steel frames, brackets, and weldments. Carbide for stainless or hardened components.
  • HVAC: HSS cutters for punching clean holes in ductwork, sheet metal, and equipment panels.
  • Structural Steel / Construction: HSS or carbide depending on steel grade; larger diameters for bolt holes in beams and columns.
  • Automotive / Heavy Equipment: Carbide-tipped cutters for hardened chassis components and high-strength steel.
  • Electrical / Plumbing: HSS cutters for conduit and pipe penetrations through steel panels or enclosures.

Summary: How to Choose

Here's a quick decision guide:

Have questions about which cutter is right for your specific application? Contact us — we're happy to help you find the right tool for the job.

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