CRL Weldon Countersinks are known for their high quality unique designs and outstanding performance. They cut chatterless finished holes in aluminum every time. Smooth drilling action from a single cutting edge no matter what angle you cut at. The 1/4" (6.3 mm) shank diameter fits any 1/4" or 3/8" drill chuck.

In other words, don't expect them to do much in steel. My impression is that, for steel at least, they are OK to deburr or even chamfer a hole, but not countersink it. The geometry changes drastically as the tool enters the hole and you rapidly get to a point where it won't cut, and it just spins.

I get better results with a cone on the end of a bit of silver steel, ground away to half the thickness, like a D-bit.

Neil

<edit> I love the marketing speak: 'single cutting edge for fast removal of stock' – it's like saying a Reliant Robin is faster because it only has three wheels.