Shoulder rest

A shoulder rest is something which is used by people who play the violin or the viola. It may be made of wood, aluminium, carbon fiber or plastic. It appeared around the middle part of the 20th century. Usually, the shoulder rest attaches to the edge of the violin with "feet" padded with rubber tubing or made of soft plastic.
The purpose of a shoulder rest is to help the player to be comfortable holding the violin, which is held between the chin and the shoulder. It is a relatively recent invention, and though it is quite commonly used among modern violinists and violists, it is not universally used. Depending on body type and style of clothes, some musicians prefer no more than a thin sponge, a cloth or sometimes nothing at all under the instrument. It is important that the player can shift his left hand easily and freely to play in the higher positions without being afraid that he will drop the instrument, and without feeling the need to squeeze the instrument between his chin and shoulder as this will make the muscles in his neck very tight.
The shoulder rest must not be confused with the chinrest, which is the bit on which the player rests his chin.