The plastic case that holds the drills from my carbide drill bit set held them so tight that I cut my fingers too many times trying to get the right size drill bit. Thought it might be worth a try and was very surprised at how quickly they cut through the 1/8" thick steel angle and those steps required applying enough pressure before it cut through the next size up. After only half a dozen Holes still feel sharp to the touch so they appear durable. As for durability, I won't know for sure until I use them more, but for now I assume they'll wear well. (What a long time may take a while since the steel construction project I used them on is complete)