Oscillating system for mechanical timepiece

An oscillating system for a mechanical timepiece, comprising:

• an annular balance wheel fixedly arranged on a rotatably mountable balance staff having an axis of rotation;
• a helical spring enclosing said balance staff and having an inner end fastened on said balance staff and an outer end;
• a fastening device, said annular balance wheel being rotatable relative to said fastening device, said fastening device having a helical-spring connector including an inner clamping jaw and an outer clamping jaw, said inner clamping jaw being arranged radially inside of said outer clamping jaw in relation to said axis of rotation;
• a clamping screw operatively arranged for bracing said inner clamping jaw against said outer clamping jaw;
• and
• a spring arm connecting said outer clamping jaw to said inner clamping jaw,
• wherein said outer end of said helical spring is arranged between respective clamping surfaces of said inner clamping jaw and said outer clamping jaw for fixedly clamping said outer end between said clamping surfaces, and
• wherein said outer clamping jaw defines an aperture through which said clamping screw is guided, said aperture being directed approximately radially in relation to said balance staff, and said inner clamping jaw defining a threaded bore arranged approximately coaxial with said aperture, said clamping screw having a screw head supportable on said outer clamping jaw and a threaded shank threadably receivable in said threaded bore in said inner clamping jaw for bracing said inner clamping jaw against said outer clamping jaw.