The present invention relates to a helically coiled torsion spring for a torsion spring based automatic injection device, coiled in a longitudinal direction (X) and having a number of consecutive windings located between a distal winding having a distal end and a proximal winding having a proximal end. Each winding further has an outwardly pointing surface. At least one end of the torsion spring is abruptly cut to form a flat end surface with no bends and at least a number of the consecutive windings are coiled with a gap between the consecutive windings such that that the torsion spring apply an axial force when the distal end and the proximal end are moved axially against each other. The invention further relates to a torsion spring based automatic injection device for expelling settable doses of a liquid drug utilizing such torsion spring to urge the abruptly cut ends into proper engagement.
