THREADING

Threading refers to all the threads — the helical ridges — that make up a screw, as well as, by extension, the operation of producing them. Each thread forms a helix wound around the cylindrical body of the screw; the distance separating two consecutive threads, measured parallel to the axis, constitutes the pitch of the screw. A distinction is made between external threading, that of screws and rods, and internal threading, or tapping, made in a hole to receive the screw. In watchmaking, threads reach an extreme fineness and follow standards specific to the profession, guaranteeing the interchangeability of screws, tiny but essential to the assembly of bridges, dials, and external parts (case, dial, hands). Threading is carried out using dies and taps, or by profile turning. Its quality — regularity of the pitch, sharpness of the threads, absence of Burr — determines the strength of the assembly and the possibility of disassembling and then reassembling a part without damaging it.