Cobalt Extra Long Drill Bits Set (5PCS) - 12in Deep Hole Drill

In this review the Cobalt Extra Long Drill Bits Set (5PCS) is evaluated for metalworkers and serious DIYers who need reliable deep hole drilling. The set's single biggest selling point is its extra long 12in length combined with M35 cobalt high speed steel construction, which makes it suited to reach deep or recessed holes in stainless steel and other hard metals without switching to extensions. For anyone tackling industrial or maintenance projects where depth and edge retention matter, this review focuses on real-world performance, durability and tradeoffs.

Key Features

• Extra long 12in length: The 12in overall length and 8in flute length let users drill deep holes in panels or assemblies without special extensions.
• M35 cobalt HSS construction: Industry grade M35 with 5% cobalt increases hardness and wear resistance compared with standard HSS for tougher metal jobs.
• 135 degree split point: The split point design prevents walking so drilling starts more accurately and often removes the need for a center punch.
• Fully ground spiral flute: Precisely ground flutes clear chips faster, reduce friction and keep the bit cooler during extended drilling runs.
• Size range included: Five common sizes from 1/8in to 3/8in cover most general deep-hole drilling needs without buying individual bits.

Who It's For

The set is aimed at metalworkers, maintenance techs and dedicated DIYers who regularly drill deep holes in stainless steel, general steel, alloy steel, sheet metal and cast iron, or who need longer reach in workshops and industrial settings. Its M35 composition and long flutes make it especially relevant for jobs where durability and chip evacuation over depth are priorities.

Users who rarely drill deeper than a few inches, or who need metric sizes or specialty coatings for extreme heat resistance, may prefer shorter, coated or different alloy bits. Also, novices should manage speed, pressure and cooling to avoid breakage when working hard metals.

Pros & Cons

Pros

• Excellent reach with 12in length for deep hole drilling in assemblies and thick stock.
• M35 cobalt construction offers improved hardness and edge retention versus standard HSS.
• 135 degree split point reduces walking and improves drilling accuracy without a center punch.
• Fully ground flutes evacuate chips well, helping keep the bit cooler during long cuts.

Cons

• Durability reports are mixed; some users report long edge life while occasional breakage has been observed on very hard impacts or improper speeds.
• Longer bits require careful speed and pressure control to avoid wobble or stress compared with shorter bits.

Specifications

Our Verdict

The Cobalt Extra Long Drill Bits Set is a solid choice for professionals and experienced DIYers who need deep hole capability and the hardness benefits of M35 cobalt HSS. It delivers precise starts, good chip evacuation and useful size coverage, representing strong value when deep reach is required; buyers should control speed and cooling to avoid occasional durability issues reported by some users.

Frequently Asked Questions

Can these bits drill stainless steel?
Yes, the M35 cobalt composition and split point design make them suitable for stainless steel when used with proper speed, pressure and cooling.

Do I need a center punch?
Typically no; the 135 degree split point reduces walking so a center punch is often unnecessary for accurate starts.

What sizes are included?
The set includes 1/8in, 3/16in, 1/4in, 5/16in and 3/8in extra long drill bits.