This is a 1/8 inch drill bit Extended-Reach. We use this for drilling a hole that will take a #4 machine screw. They can be used on carbon steel, aluminum, copper, brass, bronze, and plastic. The majority of our kits and circuit boards use a #4 machine screw so this drill bit size is a must for putting together a robot kit. A long overall length allows you to reach deep, inaccessible spots.