Bosch Cobalt metal drill bit set (14 pc)

The first time I pushed the 1/8-inch bit from the Bosch cobalt set into a stubborn steel fastener, I knew this kit had the right stuff for metal work. It cut predictably, carried chips cleanly, and didn’t squeal or burn when I kept the speed and pressure dialed in. After several weeks of drilling mild steel angle, EMT conduit, a few hardened bolts, and some incidental wood and plastic, here’s how the set has fared in my shop.

What’s in the box and how it’s built

This is a straightforward 14-piece cobalt steel set ranging from 1/16 to 1/2 inch, with two 1/8-inch bits—a smart inclusion since that’s the size most of us break first. The cobalt alloy gives these bits higher red-hardness than standard HSS, so they tolerate heat better and keep an edge longer in ferrous metals.

The grind and finish out of the case are clean and consistent. Lands are even, flutes are smooth, and the cutting lips are crisp with no burrs. Shanks are straight; I didn’t see any wobble attributable to the bits when chucked properly. It’s a basic molded case that keeps everything compact, but the sizing labels are faint and the slots are tight—more on that later.

Performance in metal

• Mild steel: The set shines here. In 1/8- to 3/8-inch holes through common angle and flat bar, the bits dig in positively and evacuate chips without packing. With light cutting oil and a moderate feed, the smaller sizes produce straight, round holes and need very little deburring.
• Harder materials: On hardened fasteners and thicker structural steel, cobalt pays off. The 1/8- and 3/16-inch bits handled pilot holes through heat-treated bolts without chattering or glazing. Running slow with cutting fluid and pecking to clear chips kept temperatures in check, and the edges held up.
• Stainless: The set will cut stainless if you respect it—slow speed, firm feed, and lubrication. I tested on thin sheet and light angle; progress was steady, and edge wear was reasonable. Expect to re-sharpen sooner than with mild steel, which is normal for cobalt bits used on stainless.
• Cast iron: Dry drilling cast iron isn’t a problem. The bits produced powdery chips and maintained cutting edges through several holes in a machine base plate.

Compared to generic HSS, these bits cut cooler and maintain bite longer. They don’t magically solve poor technique, though; run them too fast or dry on tough stock and they’ll glaze like anything else.

Performance in other materials

• Wood: They work, but the geometry is optimized for metal. In softwoods, the smaller bits track fine; larger sizes can tear the exit if you don’t back the workpiece. I wouldn’t choose them as a primary wood set, but they’re perfectly serviceable in a pinch.
• Plastics: With slow speed and a feather-light feed, they cut clean holes. Use a backing board to avoid breakout.

Speed, feed, and chip control

Cobalt responds well to the fundamentals:
- Drill press or steady hand: Clamping work and using a press lets the bits show their best. In a hand drill, a firm, consistent feed prevents skating and heat build.
- Slow it down: I ran the 1/8-inch bits below 1,000 RPM on steel, stepping down as the diameter increased. The 3/8- and 1/2-inch bits prefer slow, torque-rich rotation.
- Lubricate: Simple cutting oil makes a noticeable difference in temperature and edge life on steel and stainless.
- Peck drill: Especially over 3/16-inch, periodic chip clearing keeps flutes from packing and prevents edge galling.

Chip evacuation is good across the range. The flutes clear well, and I didn’t have issues with chips welding to the lips when lubricated.

Accuracy and hole quality

With center punching and proper clamping, the bits start predictably. Holes are on-size to slightly undersized, as they should be for clean fits; a quick ream or light deburr yields precise results when needed. The larger sizes (5/16, 3/8, 1/2) track straight if you step up through pilots rather than trying to hog from a small pilot to final size in one go.

I didn’t encounter noticeable runout beyond what’s typical for consumer chucks. If you need tolerance-critical work, pair these with a drill press and quality chuck; the bits are capable of producing clean, repeatable holes.

Durability and sharpening

Edge retention has been solid. After several dozen holes in mild steel and a handful in harder stock, the small and mid sizes still bite without requiring excessive pressure. The cobalt alloy welcomes re-sharpening. A basic bench grinder or a drill-bit sharpening guide brings the lips back quickly; the steel doesn’t burn as easily as basic HSS, but it’s still worth cooling between passes.

A note on brittleness: like all cobalt bits, they’re stiffer and a hair more brittle than plain HSS. Avoid side load, don’t pry, and let the bit do the cutting. The inclusion of a second 1/8-inch bit is practical insurance.

Case and organization

The case keeps the footprint compact and the bits secure, but it’s not my favorite. The size markings are small and low-contrast, so I had to tilt the case to catch the light or read the shanks. The slots are snug—good for retention, less good for quick changes, especially with oily fingers. It’s a minor annoyance in daily use, and I ended up using a silver marker to highlight the sizes I grab most.

Fit with common drills

The kit’s range tops out at 1/2 inch. If your drill only accepts up to 3/8-inch shanks, you won’t be able to chuck the largest bit. The rest of the set is fine for 3/8-inch chucks. On the smaller end, bits down to 1/16 inch are included and run true if your chuck jaws are in good condition.

What I’d change

• Clearer size markings. High-contrast labels or etched markings on the case would speed selection.
• Slightly wider spacing in the case. It would make removal less fiddly with gloves or oily hands.
• Optional letter/number sizes. For metalworkers who need tighter fitment with fasteners or reamers, an expanded set would pair nicely with this fractional kit.

Who this set suits

• DIYers and tradespeople who regularly drill steel, conduit, and hardware and need reliable bits that hold an edge.
• General shop use where a small, well-chosen range covers most tasks.
• Anyone tired of burning up basic HSS on steel but not ready to jump to specialty carbide.

If your work is heavy on stainless or hardened steels day in and day out, you might eventually want premium cobalt with expanded sizes or step drills for sheet. For occasional metal work, fabrication, and maintenance, this set hits the sweet spot of performance and cost.

Care tips for best results

• Always center punch metal before drilling.
• Use cutting oil on steel and stainless; drill dry on cast iron.
• Step up through sizes rather than forcing a big bit from a tiny pilot.
• Keep speeds low and feeds steady; let the chips tell you if you’re too fast (blue chips) or too slow (dusty rubbing).
• Sharpen as soon as you notice increased pressure or heat. It’s easier to touch up early than to recover a burnt edge.

Recommendation

I recommend the Bosch cobalt set. It performs the way a cobalt kit should: steady cutting in steel, good chip evacuation, respectable edge life, and clean, accurate holes when used with sound technique. The sizing range covers most common tasks, the inclusion of a duplicate 1/8-inch bit is thoughtful, and the bits sharpen well when the time comes. The case could use clearer markings and a little more room between slots, but those are minor usability gripes rather than deal-breakers. If you want a compact, capable metal-drilling set that doesn’t wilt at the first sign of hardened steel, this one earns a place in the drawer.