B

• Balance-wheel

  The regulating organ of the watch, vibrating on a spiral hairspring.  Lengthening or shortening the balance-spring makes the balance-wheel go faster or slower to advance or retard the watch, dividing time into exactly equal parts.  Each of the to-and-fro movements of the balance is called an 'oscillation'.

• Barrel

  Thin cylindrical box containing the mainspring of a watch. The toothed rim of the barrel drives the train.

• Battery

  A combination of two or more cells electrically connected to work together to produce electric energy which can then power a watch.

• Bezel

  The ring that surrounds the watch dial.  A bi-directional rotating bezel can be rotated either clockwise or counter clockwise.  These can be used for mathematical calculations such as average speed or distance of for keeping track of elapsed time.

• Bracelet

  The band which holds the case in place and encircles the wrist.

• Buckle

  The fastening for a strap, consisting of a rim and a tongue. 

• Bridge

  Complementary part fixed to the main plate to form the frame of a watch movement.  The other parts    are mounted inside the frame.