FLINQUE
Engraving on the dial or case of a watch, covered with enamel layer.

FLUTED

Said of surfaces worked with thin parallel grooves, mostly on dials or case bezels.

FLYBACK
A feature which stops a chronograph second hand and returns it to its starting position with a single push of a button. Originally, this function was developed to meet the needs of air forces.

FOLD-OVER CLASP
Hinged and jointed element, normally of the same material  as the one used for the case. It allows easy fastening of the bracelet on the wrist. Often provided with a snap-in locking device, sometimes with an additional clip or push-piece.

FOURTH-WHEEL

The seconds wheel in a going-train.

FREQUENCY

Vibration generally defined as the number of cycles per time unit; in horology it is the number of oscillations of a balance every two seconds or of its vibrations per second. For practical purposes, frequency is expressed in vibrations per hour hour (vph).

FUSEE
A conical part with a spiral groove on which a chain or cord attached to the barrel is wound. Its purpose is to equalize the driving power transmitted to the train.