An earring is a piece of jewelry attached to the ear via a piercing in the earlobe or another external part of the ear (except in the case of clip earrings, which clip onto the lobe). Earrings have been worn by people in different civilizations and historic periods, often with cultural significance. Locations for piercings other than the earlobe include the rook, tragus, and across the helix (see image at right). The simple term "ear piercing" usually refers to an earlobe piercing, whereas piercings in the upper part of the external ear are often referred to as "cartilage piercings". Cartilage piercings are more complex to perform than earlobe piercings and take longer to heal. Earring components may be made of any number of materials, including metal, plastic, glass, precious stone, beads, wood, bone, and other materials. Designs range from small loops and studs to large plates and dangling items. The size is ultimately limited by the physical capacity of the earlobe to hold the earring without tearing. However, heavy earrings worn over extended periods of time may lead to stretching of the earlobe and the piercing.