A scriber pen is a precision hand tool used by machinists and hobbyists to mark fine, permanent lines on hard surfaces like metal, glass, or plastic. It consists of a slender, pen-like handle and a sharp, tapered tip typically made of hardened steel or tungsten carbide to prevent dulling. Because it physically scratches the material rather than using ink, it provides a highly accurate layout line that won't smudge or rub off during cutting, drilling, or machining.