TORSION SPRING FIXATION IN AUTOMATIC DRUG DELIVERY DEVICE

A drug injection device (1) comprising a dose expelling mechanism for expelling drug from a reservoir through a reservoir outlet, the dose expelling mechanism comprising: a first component (40), a second component (10, 10', 15', 10", 15"), and a torsion spring element (20) for inducing relative rotation between the first component (40) and the second component (10, 10', 15', 10", 15") to execute a dose expelling operation, the torsion spring element (20) extending along a longitudinal axis and comprising: a first spring end portion (22) being rotationally restrained with respect to the first component (40), and a second spring end portion (23) exhibiting an end portion inner diameter in a relaxed state of the torsion spring element (20), wherein the second spring end portion (23) is fitted over a spring receiving portion (11) of the second component (10, 10', 15', 10", 15"), the spring receiving portion (11) having a transversal dimension which is larger than the end portion inner diameter, and the fitting of the second spring end portion (23) over the spring receiving portion (11) being configured to provide a sticking friction engagement between the two when the torsion spring element (20) is strained to exert a maximum in-use torque.