The present invention relates to a torsion spring based automatic injection device for expel- ling settable doses of a liquid drug. The spring mechanism of the injection device comprises a housing assembly and a dose setting assembly being rotatable relatively to the housing assembly and a torsion spring (1) encompassed there between such that the torsion spring (1) is strained when rotating the dose setting assembly relatively to the housing assembly. The torsion spring (1) is helically coiled having a longitudinal direction (X) and a number of consecutive windings wherein a distal winding (4) has a distal end (2) and a proximal winding (5) has a proximal end (3). Each of the winding has an outwardly pointing surface (6) together forming an outside surface of the torsion spring being parallel to the longitudinal direction (X). Either the housing assembly or the dose setting assembly or both comprises a polymeric spring receiving arrangement, which arrangement comprises a first surface (23) substantially parallel with the longitudinal direction (X) of the helical torsion spring (1) for abutting the distal end (2) or the proximal end (3) of the helical torsion spring (1) and which arrangement further comprises a second surface (24) substantially parallel with the longitudinal direction (X) of the helical torsion spring (1) for supporting the outwardly pointing surface (6) of the at least distal winding (4) or the at least proximal winding (5).