Bearing for a piston rod body for a drug delivery device, a piston rod arrangement and a piston rod body

A drug delivery device comprising:

• a cartridge unit comprising a cartridge retaining member, the cartridge retaining member being configured to retain a cartridge therein, the cartridge having an outlet at its distal end, wherein the cartridge contains medication therein and a bung (10) is disposed within the cartridge, the bung being movable in a distal direction with respect to the cartridge to dispense medication from the cartridge through the outlet of the cartridge during operation of the drug delivery device, and
• a drive mechanism comprising a housing and a piston rod arrangement retained in the housing, the piston rod arrangement comprising a piston rod body and a bearing axially fixed to the piston rod body, the piston rod body being rotatable relative to the bearing, wherein the bearing has an axis and comprises a first surface, a second surface, and a third surface, wherein the first surface is axially spaced apart from the second surface, and the third surface connects the first and second surfaces, wherein each of the first and third surfaces defines an opening, and the opening in the first surface is connected to the opening in the third surface,
• wherein the cartridge unit and the drive mechanism are releasably secured to one another, wherein the cartridge retaining member is provided with a fixing member for attaching the cartridge unit to the drive mechanism, and wherein a proximal end portion of the cartridge unit is configured to be secured to a distal end portion of the housing,
• wherein the piston rod arrangement is configured to transfer a force to the bung to distally displace the bung with respect to the cartridge to dispense a dose of the medication from the cartridge, wherein the second surface of the bearing is formed by a bung contact wall which is arranged to abut a proximal end face of the bung, and
• wherein the drug delivery device is a needle-based pen-type injector.