Irwin Tools 3016021 Single Cobalt Alloy Steel High-Speed Steel Drill Bit, 21/64" x 4-5/8"

Perfect recommended size to use with a Helicoil 8X1.25mm thread repair kit. Holes are clean (in aluminum) and crisp.

Tried using an HSS bit to enlarge a stainless steel header flange bolt hole. Took forever and made bit and flange red hot to get one hole done. This bit enlarged a hole in about 45 seconds. Did the other 4 in just a few minutes. So if you are wondering if you need m35 or m42 cobalt drill for stainless steel, this m35 which is supposed to be 5% cobalt worked great. And 1/3 the price of the m42 cobalt bit.

It drilled a smooth accurate hole in my metal project and didn't show any signs of dulling. What more can I say?

Seems like an ok bit. Didn't work very well for my application. If you are trying to drill out a ratchet head this is not the bit for you. Advertised as 8% cobalt and package clearly states 5%

Good quality drilled great price

Great price, and it has the cobalt inside the metal not just coated. This bit took 6 hours of drilling through a Jeep bumper for 4 bolts. It also had to drill through the steel tube in back of the bumper also. Slow speed and oil really helped. Still sharp. Would buy again. Made a very hard job do-able. Irwin brand has a really good rating. I try to purchase Irwin before other brands because of their quality and low price. *****

After dulling two other “Cobalt” bits and one other HSS bit drilling through a Grade 8 Bolt, this Irwin did the job in one try! A little cutting oil and peck drilling and it finished the job -3/8” through the Bolt with ease. Cuts well. Only used it on this one job, but I expect it will last. Better than other, more expensive options.

Very good quality drill bit.

Good quality for the price...

Broke it on the second hole...it was not even drilling straight, i then finished my work with a cheap drill bit from any hardware store and over 50 holes without an issue...bad experience with this expensive product, I’m very disappointed and i don’t recommend it to no one

Not too sure what to say here. They work like they should and they have not broke on me.

Using a large floor-standing drill press running at it's near-slowest speed and adding drops of oil often (often!) to keep the friction heat down, we easily drilled 16 holes with this single bit (no pilot holes, we just went full size right off the bat) and I'd dare say for sure that the 16th hole went as quickly and easily as the 1st hole. Wayyyyy easier than I'd ever experienced with all my cheaper drill bits I've bought over the years.

good to go