HSS Cobalt Step Drill Bit Metric 4mm to 32mm , 15 Steps, Shank 3/8"

I bought this bit mostly for the 12 mm. section, which is just right for many electrical toggle switches. The 12 mm. section is quite accurately sized. One of the steps on the way to the 12 mm. section was very slow drilling in steel sheet metal, and the starting point did not cut well. The steps on this drill bit are generously sized for thicker materials than some step bits , and the step sizes are clearly labeled. The range of 4 mm to 32 mm is quite large. Step bits are almost a requirement for safely drilling through sheet metal , as they don't grab the work as do conventional large drill bits. It helps to first drill a small pilot hole with a conventional bit before you use the step drill. But now the bad news; after drilling only three holes in sheet steel, the cutting edges show deep grooves and dulling. My other step drill bits have drilled dozens of holes in this same steel without damage. This bit is not made of good steel, and the cobalt nitrite coating has already worn off . I may just have a bad sample, but I don't know. This bit is more suitable for drilling in aluminum , brass, or plastic. If you do drill into steel, use lots of cutting oil.

This is a great light duty bit. Great price.