B

Balance -

The heart of a mechanical watch movement. The mainspring provides the energy. The hairspring, coupled to the balance, makes it swing to and fro, dividing time into equal parts. Each to and fro movement of the balance is called an oscillation. One oscillation is composed of 2 vibrations.

Balance Spring - also called "hair spring". A very fine spring in a mechanical watch that returns the balance wheel back to a neutral position.

Bar (Spring Bar) - a thin metal rod fixed between the horns for attaching the wristlet.

Barrel -

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

Battery - The energy needed to drive a quartz watch.

Battery Reserve Indicator - EOL - end of life. Indicates pending battery failure.
One method of warning is to see the seconds hand jumping 2 seconds at a time.
see Power Reserve Indicator

Bevel - cut down sharp edges

Bezel - the ring around the crystal on the top portion of a watch. Usually made of metals such as gold, gold-plate, platinum or stainless steel. Holds the glass or crystal in place.

Bi-directional Rotating Bezel - a bezel that can be moved either clockwise or counter-clockwise. Used to make mathematical calculations or keeping track of elapsed time.

Blued Screws - screws that are "blued" by either heat or chemicals for decorative purposes.

Bombe - French for "convex" and refers to rounded or domed shape.

James Bond watch -

The Seamaster Professional with reference number 2531.80.00
is the watch worn by James Bond in the Bond movies.
This Seamaster is made of stainless steel on a stainless steel bracelet, fitted with a blue dial, unidirectional rotating bezel with blue ring and a sapphire crystal.
It has a diameter of 39.3 mm and is equipped with calibre 1120 self-winding movement with official chronometer certificate.
It is waterproof to 300 metres.

Bracelet - a metal link watch band

Braille Watch -

Crystal can be lifted. The numerals protrude allowing the time to be told be feel for the visually impaired.
Also known as a Tact watch (tactile)

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

Bubble Back - term given to the case back of the first style automatic watches by Rolex due to it's bubble-shaped screwed case back.

Bumper Wind - Automatic watches with winding weights (rotors) that were restricted to turning 270 degrees. The weights then "bumped" off the bumper springs at either end.

Butterfly Clasp -

2 ends of the buckle on a bracelet fold over into the centre.
On a deployant clasp (see deployant) one end folds over the full length.

Buttons -

piece on the outside edge of a watch case, such as
a chronograph, to activate various functions.