An injection device includes a housing (40) for containing a syringe or cartridge (14) of medicament; a rotary drive shaft (20) for being rotated by an adjustable preset amount to cause expression of a corresponding amount of medicament from the syringe or cartridge; a torsion drive spring (24) anchored at one end region relative to the drive shaft (20) and, at its other end region being secured to a fitting (44) adapted to non-rotatably engage a seat (48, 50) on the housing.