Balance spring boot

A balance spring boot, arranged to be driven onto an index for adjusting a timepiece balance spring, wherein the index is arranged to be pivotably mounted relative to an axis parallel to the pivot axis of said balance spring or merged therewith, said balance spring boot includes two pin shoulders, which are parallel to each other in one direction, separated by a distance, and arranged to limit the radial beat of a balance spring inserted between said pin shoulders, and also polished to support said balance spring with minimum friction;

• said balance spring boot includes a means for resting on said index arranged, in the position in which said balance spring boot is mounted on said index, for adjusting said direction of said pin shoulders, parallel to said pivot axis of said index, wherein said balance spring boot includes a sight hole in a parallel direction to said direction of said pin shoulders, said hole being clear to allow visualisation by an operator or an optical instrument of said pin shoulders, and the portion of a balance spring inserted between said pin shoulders at a distance from and/or in contact with one and/or the other of said pins.