These small drill bits are good for wood, plastic and thinner metals. Being 1-3mm in diameter, they work with most rotary tools and can run at high speeds. I mainly use them for 3D printed plastic parts and these bits work well for that use. I've also tried them on a tree and they work well. The bits don't seem strong enough for thick metal, but I don't think thinner sheet metal and mild steel bar would be too much of a problem, although you'll want to use a slower speed and lube to cut metal. I'm happy with these overall. They come in little plastic bags and I ended up storing them in a little plastic box to keep them organized. You get 10 drill bits of each size and it's hard to beat the price for so many decent quality small drill bits.