The bridges () used to be made of ivory, but nowadays are typically made of plastic, and occasionally made of wood. One can alter the pitch of a string by manipulating or moving the bridge. For some very low notes, there are small bridges made, as well as specialty bridges with three different heights, depending on the need of the tuning. When a small bridge is unavailable for some very low notes, some players may, as an emergency measure, use a bridge upside down, though this is unstable and not ideal. Bridges have been known to break during playing, and with some older instruments which have the surface where the bridges rest being worn due to much use, the bridges may fall during playing, especially when pressing strings. There are, of course, various sorts of patch materials sold to fill the holes which cause the legs of a bridge to rest on an unstable area. About long and wide, the is traditionally placed on the floor in front of the player, who kneels.