HAND-FITTING TOOLS
WHAT IS THE USE OF HAND-FITTING TOOLS?
Hand-fitting tools designate the manual pushers used to set the hands onto their respective seats — cannon-pinion for the minute hand, hour wheel for the hour hand, extended pivot of the seconds wheel for the sweep second hand, etc. — during the final stage of casing the movement. Entrusted to simple hand-held instruments, the operation nevertheless demands absolute precision: the hand, friction-fitted onto its pipe, must be pressed perfectly flat, without deformation of its body or marking of the dial beneath. The gesture tolerates neither lateral slippage nor excess pressure, and requires a force perfectly perpendicular to the plane of the dial — which justifies the existence of a family of specific tools adapted to each type and dimension of hand.
The hand-fitting pusher classically takes the form of a fine cylindrical rod, most often with two active ends, mounted on a handle that allows a supple and precise grip. Each end carries a small central hole, drilled and chamfered in an insert of a suitable material — brass, Delrin, PEEK or nylon —, calibrated to the diameter of the hand’s pipe to be fitted. The double end allows two different diameters to be used, for example those of the hour hand and the minute hand; the handles are frequently coloured or marked to identify quickly the dimension associated with each tool.
These pushers are sold individually or in sets, generally presented in a case covering the usual calibres, from the very fine diameters of small-second or chronograph hands to wider seats.
Hand-fitting tools are used at the very last stage of movement assembly, after reassembly of the gear train, fitting of the dial and preparation of the hands. The operation is carried out by hand, at the workbench, the watchmaker holding the movement with one hand and applying the pusher vertically with the other, while monitoring the flatness and concentricity of each hand under a loupe. The correct choice of diameter, the cleanliness of the pusher’s tip and the regularity of the pressure determine the result: a poorly fitted hand will warp, rub against the dial or the crystal, hinder the passage of the other hands, or quickly loosen in service.