Torsion spring mechanism for medicament delivery device, and medicament delivery device comprising said mechanism

A mechanism for a medicament delivery device, the mechanism comprising:

• a base structure;
• a plunger rod movable relative to the base structure along a longitudinal axis;
• a driver rotatable relative to the base structure about the longitudinal axis and engaging the plunger rod;
• a torsion spring having a rotatable end connected to the driver and a base end connected to the base structure, the torsion spring being arranged to rotationally drive the driver;
• and
• at least one support part arranged to support the torsion spring in a lateral direction with respect to the longitudinal axis, wherein the at least one support part comprises a second part, and a first part rotatable about the longitudinal axis relative to the base structure and relative to the second part,
• wherein the mechanism comprises at least one rotational interface between the driver and the base structure, and
• wherein the at least one rotational interface is positioned at between 0.5% and 99.5% of a length of the torsion spring along the longitudinal axis from the driver to the base structure.