I use an older in. 3/8 one that says 605 on the shank. It is harder, so more brittle, but necessary for harder steel.

Could not drill even one hole through a thin Stainless Steel ruler. Advertised as lasting 4x longer when drilling SS...really??

Cobalt bits are recommended for drilling into hardened steel. I need to drill 8 holes in knife tangs I'm making. I spend the whole evening and could drill 1 hole with 2 of these bits. I used a honing oil with one and 3N1 oil with the other. I barely have a scratch on the tang.

[This review was collected as part of a promotion.] I’ve used a variety of different kinds of DEWALT drill bits, and while these are often more expensive than generic cobalt or M42 drill bits, they are high quality. I see several other reviews that are giving these bits low numbers due to breakage. Well, I think that is a reflection upon the user rather than the bits. The reality is, these bits are very hard and thus very brittle. While you can use them in a hand drill, you have to be extremely careful as any binding can result in a snap. These bits are best suited for use in a press or mill. Nothing particularly special regarding this specific brand, but just an inherent attribute of the high cobalt steel. To this end, if you don’t need a cobalt bit, a Ti-coated or HSS may be a better choice if you’re not going to be careful, as softer materials can actually cause binding more frequently than harder materials where these specific bits shine. While you absolutely can use these in wood or aluminum, they aren’t going to function any better than a high quality HSS bit. So, choose the correct tool for your application. Then use it properly. Even then, you will still break a bit on occasion. It’s a consumable tool.