I used this bit to drill holes in hardened knife tangs for pinning handle scales. It is a VERY sharp bit and drilled perfect holes with no burrs on the back side as long as I backed the blade with a piece of aluminum or mild steel. I am very impressed with this drill bit. I drilled over 40 holes in hardened 15N20 steel and it hasn't dulled at all. I would have liked for it to be longer, but as hard as it is I don't think it will need sharpened very often and should last me a few years.This drill bit did the job that other drill bits could not. It drilled right through a very hard material that ruined some other bits that advertised as ""super hard" or "super strong". Be sure to set at slower speed and use plenty of cutting fluid to protect your investment. Love it.The bit works like magic... the job was done faster and easier as expected. AAA+++This bit handled drilling out a broken Zerk fitting my ordinary drill bits wouldn't touch. Good vendor.Total life saver. After killing several other bits of all other materials, including cobalt, This one drilled my D2 Tool steel just fine. THANK YOU!Wow! Super fast shipping. Just what I was looking for.They cut good when new but dull fast and are super brittle. An experienced machinist would have no trouble with them.GREAT SERVICE AND PRODUCT DID AS DESCRIBED