Drill America #4 Cobalt Heavy Duty Drill Bit Pack of 12 - Durable

In this review the Drill America #4 Cobalt Heavy Duty Drill Bit (Pack of 12) is judged as a workhorse set for machinists and tradespeople who need reliable performance when cutting tough metals. The bottom line: it is best for users who regularly drill stainless steel, nickel alloys or other high tensile materials because the cobalt steel formulation holds heat and hardness under heavier cutting loads. The pack of 12 offers good value for shops and hobbyists who prefer jobber length bits that combine durability with versatility.

Key Features

• Cobalt steel construction: Provides improved red hardness so the bits maintain cutting edge and can run hotter than standard high-speed steel when drilling hard alloys.
• Gold oxide finish: A thinner surface treatment that identifies the tool and offers corrosion resistance without changing cutting behavior compared with uncoated bits.
• Spiral fluted right-hand cut: Evacuates chips up and out of holes to reduce clogging and keep holes cleaner during continuous work.
• Round shank design: Fits a wide variety of chucks and toolholding systems for easy switching between handheld drills and drill presses.
• Manufactured to NAS 907: Built to a recognized aerospace standard, indicating consistent geometry and quality suitable for demanding applications.

Who It's For

This set is aimed at metalworkers, mechanics, and serious DIYers who frequently drill high tensile materials like PH stainless, inconel or titanium and need bits that hold hardness and cut reliably under higher speeds. The twelve-piece pack suits small shops or individuals who want backups and repeatable performance without purchasing single specialty bits.

Those who primarily drill soft materials, wood, or occasional light-duty metal might look elsewhere for cheaper carbon or HSS options, and users needing carbide performance for production CNC work should consider solid carbide tools rather than jobber-length cobalt bits.

Pros & Cons

Pros

• Excellent durability and edge retention in hard metals thanks to the cobalt alloy.
• Good value for money when buying a 12-piece pack for shop rotation and replacements.
• Thin gold oxide finish provides basic protection while keeping cutting action similar to uncoated bits.
• Round shanks and standard jobber length make these bits versatile across machines.

Cons

• Not coated with thicker performance coatings, so users wanting extreme wear resistance may prefer other surface treatments.
• Angle feedback in reviews is mixed, so hole entry geometry may vary slightly between pieces.

Specifications

Series	D/ACO
Material	Cobalt steel
Finish	Gold oxide
Shank type	Round shank
Length	Jobber length
Manufacturing standard	National Aerospace Standard 907
Pack quantity	12 pieces

Our Verdict

The Drill America #4 Cobalt Heavy Duty Drill Bit pack is a practical, cost-effective choice for anyone who needs dependable drilling in tough alloys; its cobalt build and jobber length deliver long life and versatility in workshop settings, making it a smart buy for metalworkers who value durability and predictable performance.

Frequently Asked Questions

Are these bits good for stainless steel?
Yes, the cobalt alloy and higher red hardness make them well suited for drilling stainless steel and other high tensile materials.

Will the gold oxide change cutting performance?
No, the gold oxide is a thin surface treatment that mainly aids identification and basic corrosion resistance without altering cutting behavior.

Can these bits be used in a hand drill?
Yes, the round shank and jobber length allow use in a wide variety of chucks and handheld drills as well as drill presses.