The plastic case that holds the bits from my carbide drill bit set holds them so tightly that I cut my fingers trying to get the right size too many times When I I thought it was worth a try and was very surprised at how quickly they cut through 1/8" thick steel angles and are graduated so you had to push enough until they cut through the next size up. After only one With half a dozen holes they still feel sharp so they seem durable.As for durability I won't know for sure until I use them more but for now I assume they will wear well (which is long may take a while since the steelwork project I used them on is finished).