Review on Ultimate Precision: Double Cut Carbide Rotary Burr for Finest Material Shaping by Phil Casey

I used 1/4" drill bits to open holes in 1/8" sheet steel. More than a few times the material caught so hard on the burr that the burr popped out of the material and the mill stopped. I thought the burr was definitely broken but upon inspection everything was fine. Not broken. Don't bend. The hardness is also very surprising. The millstones I have used have retained their sharpness despite some wear and tear. I would buy this item again and recommend it.