Retaining rings and other rings are usually used to fasten parts such as bearings to prevent them from coming off. They are attached using special tools such as snap ring pliers. Rings attached in the direction of thrust include shaft rings that fasten outside the part being secured, and hole rings that fasten inside the part being secured. Rings attached in the radial direction are attached at a right angle to the axial direction, enabling them to fasten parts such as bearings. Retaining rings and other rings are all available in a variety of shapes, so should be selected to match the part to fasten. The available shapes include Type C, Type R, beveled rings, Type E crescent rings, Type U and Type K. Most retaining rings and other rings are made of materials with superior hardness such as steel, stainless steel and oil tempered wire.