The twist drill is the most widely used and widely produced kind of drill bit. The term twist drill generally refers to the kind of drill bit used, not to the drill itself. A twist drill bit is a metallic cylinder with helical grooves that spiral up the bit. Drills are used in a wide variety of projects and fields, from home repair to arts to large-scale construction projects.
The twist drill is widely used because of its low price, low maintenance, and ease of use. The bits of drills are very inexpensive, and can be thrown away when they break or wear out. There is no need to sharpen or repair them when replacing them costs far less in time, energy, and possibly money. These drills are also very easy to use, allowing most individuals to use them without any kind of special training. Most modern drills are electrical and motorized, so the user does not need to expend any more effort than that which is necessary to keep the drill straight and pointed in the right direction.
Twist drill bits are designed according to the specific purpose they are to be used for and the kind of material they will drill through. The angle of the point of the bit is especially important. Most drill bits have a 118 degree angle at their tip; this angle is suitable for drilling through most materials fairly effectively. Sharper angles around 90 degrees are often used for drilling through soft materials such as soft wood or plastic. Wider angles, often around 150 degrees, are used for drilling through tough materials such as stone and metal.
A twist drill can be made out of a wide variety of materials, depending on its purpose. Most are made out of durable high-speed steel, which can endure high temperatures without losing its hardness. For particularly heavy-duty work, diamond can be added to the normal steel of the drill bit for added durability. This is seldom done, however, because of the high cost.