Review on 4.2Mm 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 by Brian Lee

I needed to install a roof rack on my truck which required drilling 12 holes in the roof. Once I got started, I discovered that I had to drill through 2 layers to get the appropriate depth, not just one. But this drill bit went through the second layer just easily as the first. I ended up with 12 very clean holes. They were perfectly sized, as the inserts I was using went in nice and snug.If you're needing to drill for a GM truck roof rack, the this is the correct size drill bit for the Rivnut inserts. My roof rack is holding very well, because this drill bit made the right size holes for it.