Bosch CO2148 21/64 in. x 4-5/8 in. Cobalt Drill Bit

Great for hard metals, excellent product.

Superior to Milwaukee, used to drill stainless first bit lasted 8 holes. Milwaukee was trash over 2

Works great

I've only tested it a few times on some thick steel angle iron, and once on stainless, but it showed no sign of dulling. It drilled through it like butter, after my cheap harbor freight drill bit just sat on the surface making a hot divot instead of a hole. I used cutting fluid (WD-40 or water works if you don't have your tapping fluid around), and I always recommend cutting fluid as well as stopping to cool before there's any smoke or smell of hot metal/fluids. Getting a drill bit too hot is the best way to ruin it, besides using it as a pry tool. I drilled right through a stainless steel hose clamp, which my cheap titanium coated bits won't even make a dent in. The price is great, and the bit definitely cuts into hardened steel like a champ. I'll be using these for drilling easy out holes and whatever else I need. I haven't checked the dimensional accuracy, but it has no visible bend or wobble. I will say it walks around instead of starting where I want it to, unless I use a center punch. That is not a problem for me, because I normally do use a spring loaded center punch, but I have noticed some bits walk more than others. I would say this one walks a bit more than the cheap, soft ones, but once it starts biting it goes right through your steel. I'll be ordering some of these in the common sizes I drill for tapping holes (for me, that's 5/16", 1/4", 3/8", 4mm, 6mm, 8mm). I'm not sure this brand offers metric sizes, but I'm going to look. Disclaimer: I'm not a machinist, and no expert on drilling. I'm just a hobbyist that does a lot of customized repairs around the house, RV, Jeep, and motorcycle.

First use, very sharp and bored the hole quickly. But the curious thing is they don't have any indications of the drill sizes on the case, so you are left with using calipers, a drill guide, or taking a guess what the diameter is of the individual bits. Even cheaply made sets indicate what the size in the position is at the positions, but not this Bosch kit.

Has stood the test of time and need.

The bolt that secures the drive shaft to my Ironman elliptical broke in the flywheel mount. The bolt was threaded on the shaft and would not unthread. Can't find a replacement shaft so the only option was to drill out the center of the broken bolt and use an extractor to remove it. I set my drill press to the slowest speed and used cutting oil. I bought a set of cobalt Milwaukee bits (Home Depot) that barely scratched the surface. Discovered that they weren't even sharp out of the box! Used a bit sharpener and cutting oil to make very slow progress, one bit step up at a time. Several of the Milwaukee bits broke off and had to be re-shaped and sharpened. The extractors would NOT budge the broken bolt. I even bought a $40 Dewalt cobalt bit from Lowes and realized that I was going to have the same issue. I decided to take the risk with ordering these from Amazon. These Bosch bits tore straight through the broken bolt (without the need to sharpen!). Never could get the extractor to move the broken bolt, but after enough of the center of the bolt was cored out, the small layer of threads remaining were knocked out with a punch. Elliptical is back in service with new bolts and fasteners. I also bought a 1/2" bit that I never used, but I'm saving that for my next emergency. These are good sharp bits.

Excellent quality. As advertised.