LingGan 5mm Metric M35 Cobalt Steel Extremely Heat Resistant Twist Drill Bit of 2pcs with Straight Shank to Cut Through Hard Metals Such as Stainless Steel and Cast Iron, 5% Cobalt M35 Grade HSS-CO

buena calidad

Seems okay. Not the best drill bit I've ever seen, though.

Used with cutting oil and drilled threw tempered still

I had to drill lines of holes for 5mm fasteners along the work hardened edges of stamped 3mm thick steel parts. Because the material was so thin compared to the hole diameter, and because 2.4mm pilot holes had been pre-drilled (a mistake), the drill would catch every time it started to break through the material. In spite of having to reverse the drill multiple times and hit the material repeatedly each hole to break through, I got 64 holes drilled with only minor chipping on one flute of a single drill.

The 4mm and 5mm drill bits that I bought from this excellent vendor are very well made. I used the 5mm to widen the axle hole in a cast iron piano pedal. The hole was very clean because the bit is extremely sharp. The 5mm brass sleeve fit perfectly. The brass axle I installed with Titebond 660 made the repair permanent and now the pedal functions as it was designed. The item description was exactly correct. Thanks for helping me.