Drug delivery device

A drug delivery device comprising:

• a housing having an opening;
• a drug storage container having an inner surface at least partially defining a drug storage chamber, an outer surface defining an outer diameter, a plunger stopper, and a delivery member having an insertion end configured to extend at least partially through the opening during a delivery state;
• a plunger rod;
• a drive mechanism configured to generate a force for driving the plunger stopper in a distal direction to expel a drug from the drug storage container through the delivery member, the drive mechanism having an inner surface with an inner diameter greater than the outer diameter of the outer surface of the drug storage container;
• and
• a force transmitter functionally coupled with the drive mechanism and the plunger stopper to transfer the force of the drive mechanism to the plunger stopper,
• wherein the force transmitter includes an inner cylindrical shell and an outer cylindrical shell, wherein at least the outer cylindrical shell is configured to move with respect to the housing.