A pen-type drug delivery device, comprising: - a dose setting member ; - a cartridge holder , wherein said cartridge holder is secured to said dose setting member ; - a cartridge including a generally tubular barrel extending from a distal end to a proximal end , the distal end being defined by an inwardly converging shoulder , a sleeve or ferrule located at the distal end , a smaller diameter neck projecting distally from the shoulder of the barrel and a pierceable seal or septum securely mounted across the open distal end defined by the neck and held in place by the sleeve or ferrule , - a locking mechanism comprising a main body , - the locking mechanism attaching the cartridge within the cartridge holder , - the main body having an outer diameter and a centrally located aperture , which extends from a proximal end to a distal end of the main body , - at least one bendable feature provided on the main body , the bendable feature comprising a first section , a second section , and a third section , the first section and the third section being affixed to the main body , - the bendable feature being movable from a first position , in which at least a portion of the second section of the bendable feature extends beyond the outer diameter of the main body , to a second position , the portion moving toward aperture until the bendable feature snaps into the second position , in said second position , at least a portion of said bendable feature being provided to retain said cartridge within said body when the aperture is placed over the sleeve or ferrule , characterized in that - the bendable feature deforms with the second section moving toward the aperture until the bendable feature snaps into an inverted position, and - a non-return feature is provided on the main body , the bendable feature moving from the first position past the non-return feature to the second position and being held in the second position by the non-return feature . - a dose setting member ; - a cartridge holder , wherein said cartridge holder is secured to said dose setting member ; - a cartridge including a generally tubular barrel extending from a distal end to a proximal end , the distal end being defined by an inwardly converging shoulder , a sleeve or ferrule located at the distal end , a smaller diameter neck projecting distally from the shoulder of the barrel and a pierceable seal or septum securely mounted across the open distal end defined by the neck and held in place by the sleeve or ferrule , - a locking mechanism comprising a main body , - the locking mechanism attaching the cartridge within the cartridge holder , - the main body having an outer diameter and a centrally located aperture , which extends from a proximal end to a distal end of the main body , - at least one bendable feature provided on the main body , the bendable feature comprising a first section , a second section , and a third section , the first section and the third section being affixed to the main body , - the bendable feature being movable from a first position , in which at least a portion of the second section of the bendable feature extends beyond the outer diameter of the main body , to a second position , the portion moving toward aperture until the bendable feature snaps into the second position , in said second position , at least a portion of said bendable feature being provided to retain said cartridge within said body when the aperture is placed over the sleeve or ferrule , characterized in that - the bendable feature deforms with the second section moving toward the aperture until the bendable feature snaps into an inverted position, and - a non-return feature is provided on the main body , the bendable feature moving from the first position past the non-return feature to the second position and being held in the second position by the non-return feature . <EOS>