BOSCH CO21 21-Piece Assorted Set with Included Case Cobalt Metal Drill Bit with Three-Flat Shank for Drilling Applications in Stainless Steel, Cast Iron, Titanium, Light-Gauge Metal, Aluminum

Worked well for what I need you to do. Bites well

5/27/2026 : great drill bits. Nice storage. Awful labeling. I had to use tape and marker to label these for myself. Bosch really needs to fix this. Already some numbers were hard to read after a little dust got on the case. Even the labels on the bits are nearly impossible to read. Why Bosch? Who are those labels meant for? People who WANT to make silly errors, and make life so much harder than it needs to be. Take my advice. Label it carefully yourself in five minutes, and save yourself HOURS of cumulative time trying to figure out which size is which.

Good value for the money. I use these bits to drill mild steel and aluminum and haven’t noticed any major wear on them so far.

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.

I haven't had a chance to really use these yet. I have a set of older bits I am trying to use up before breaking into these new bits. I have used it a couple times and I wasn't as impressed with the drill speed given other reviews and videos on them. I think they did just fine and better than most but not by a large or even meaningful difference. I haven't used it on a lot of material types, so it may be better suited for something I haven't tried yet.

Works as advertised

Good seller, fast shipper.

Got to replace some I broke in a kit of bits I have.

Watch the price going up and down . Tuesday was £39, Wednesday £29! Ive just used them and they are the tits. All the others I've tried were useless. Used with cutting oil to keep the heat down. I melted my other drill bit!

great

Excellent

These are the drill bits you want. I’ve had so many different sets from different manufacturers over the years. These were the set that impressed me. I would buy again. But I don’t think I’ll have to, they seem like they are going to last along time.

The 5/64, 7/64 and 9/64 inch sizes are basic smaller drill bits. They are ones you are most likely to break in a bit set. So you will likely have to go shopping for replacements for broken bits in these sizes. I recommend the reasonably priced Dewalt DWA1205 and DWA1207 for the first two sizes and the Bosch CO2136 for the 9/64 inch. All are available from Amazon.