The sound holes of string instruments are called f-holes due to their similarities to the letter they are shaped like, f-holes or c-holes. The instruments of the violin family (violin, viola, cello and contrabass) have f-holes. The sound holes of the Gambas are often c-shaped, thus their name c-hole. These sound holes are the acoustic center of the instrument and it is between them that the bridge is placed. The f-holes are accentuated by having additional f-grooves pointing either inward or outward.