Method for press-rolling a mainspring, from a wire comprising a pre-formed eye, utilising a roller press comprising a first support and guide means exerting a force on the wire in a first contact area located between a second and a third contact area comprised in a second and a third support and guide means, in order to wind, beyond the eye, an accumulation area with an opposite curvature to that of the eye, and wherein, as the wire advances, the position of the first contact area is gradually moved away from the second and third contact areas, to vary the press-rolling radius from a first minimum value to a second maximum value at a neck junction between the accumulation area and the eye.

A mainspring includes a spiral metal strip and a hooking area formed in an inner face of an inner end of the strip, the hooking area including at least one shaped portion and at least one cavity in the inner face of the inner end.

Method for press-rolling a mainspring, from a wire comprising a pre-formed eye, utilizing a roller press comprising a first support and guide means exerting a force on the wire in a first contact area located between a second and a third contact area comprised in a second and a third support and guide means, in order to wind, beyond the eye, an accumulation area with an opposite curvature to that of the eye, and wherein, as the wire advances, the position of the first contact area is gradually moved away from the second and third contact areas, to vary the press-rolling radius from a first minimum value to a second maximum value at a neck junction between the accumulation area and the eye.

A mainspring including a spiral metal strip and a hooking area formed in an inner face of an inner end of the strip, the hooking area including at least one shaped portion and/or at least one cavity comprised in the inner face of the inner end.

A tool for separating a plate of balance springs after winding in, including substantially parallel lower and upper rolling surfaces which are movable relative to one another, vertically or longitudinally, in order to deform the plate by ovalisation, and to subject it to a rolling movement between the rolling surfaces, and further relates to a method for separating balance springs from a plate using this tool in order to mechanically crush it in the elastic range and initiate sequences of compressing and rolling the plate.