Let Down Key this tool is a Swiss made Bergeon tool designed for the true craftsman. Letdown Key is a specially designed key for disarming and arming (winding) clock mainsprings. Let Down Key kit includes a removable metal handle, 24 numbered chucks with winding squares from number 000 to number 21 (1.75 to 7.50 mm). The complete range of possibilities you as a clockmaker will encounter, as well as a special winding chuck for alarm clocks, all well organized in a hinged wooden box. A tool for the professional!