Drum shells are commonly made of wood, metal, or pottery. The heads, made of animal skin or plastic, are fastened to the shell by nails, glue, buttons, pegs, laces, or a cord wrapped around the border of skin that overlaps the shell. Double-headed Western orchestral and band drums, such as the snare drum, tenor drum, and bass drum, usually have two hoops for each head, one around which the excess skin is lapped, another pushing against the first hoop and holding the skin taut. Lacing may be done in a W or Y pattern, adding more tension to the heads. In modern drums the lacing may be replaced by tension screws attached to the top hoop.