BEAT. The multiple sound of the escapement action heard as the 'tick'.
BEETLE HAND. The type of hour hand faintly resembling a stag beetle. See POKER HAND.
BEZEL. The rim holding the glass.
BIMETALLIC. Formed of two metals, brass and steel, whose different coefficients of expansion are utilised for compensating the effects of temperature changes on a steel balance spring. See BALANCE. Prior to the bimetallic, cut balance, a bimetallic strip, formed by riveting or fusing, was utilised, which bent under the influence of temperature changes. This strip was known as a compensation curb (q.v.).
BOTTOM PLATE. See TOP PLATE.
BOUCHON. Also 'Bush'. Hard brass tubing inserted into watch plates to form pivot holes - i.e. bearings for pivots.
BOW. The metal ring hinged, pivoted or looped to the pendant (q.v.) of the watch case, by which the watch may be attached to a chain or fob.
BREGUET BALANCE SPRING. See BALANCE SPRING.
BREGUET HANDS. Hour and minute hand slightly tapered, the end a disc eccentrically pierced to form crescent. Also called 'moon hands'.
BREGUET KEY. A watch key in which the upper and lower portions of the shaft are connected by a ratchet clutch kept in gear by a compressed spring, so that the upper part will turn the lower part in the correct direction for winding, but if the upper part is turned in the opposite direction, the ratchet slips without moving the lower part. This ensures that no damage will result from turning the key in the wrong direction. This key is also called a 'tipsy' key, presumably since it ensured a watch against damage when owned by inebriates! A similar form of key was patented in England in 1789 by S. B. Harlow.
BREGUET OVERCOIL. See BALANCE SPRING.
BREGUET STOP-WORK. This form of stop-work (q.v.) has two toothed wheels, one of eight teeth fixed to the barrel arbor and one of ten teeth fixed to the barrel itself. Projections on the two wheels meet after four turns, thus limiting the extent to which the mainspring is wound.
BRISTLE. See HOG'S BRISTLE.
BULL'S EYE GLASS. A flattened dome glass in shape, but with a small circular flat ground in the centre.
BUSH. See BOUCHON.
BUTTON, WINDING. Round, or rounded, knurled or milled button fixed to a shaft or stem by which a watch is wound or the hands set. Sometimes called a 'set-hand button'. Used in keyless watches.