The invention refers to
a pen-type injector comprising a housing (4);
a piston rod (20) adapted to operate through the housing;
a dose dial sleeve (70) located between the housing and the piston rod, the dose dial sleeve having a helical thread (74) of first lead;
a drive sleeve (30) located between the dose dial sleeve and the piston rod, the drive sleeve having a helical groove (38) of second lead;
wherein the first lead of the helical thread (74) and the second lead of the helical groove (38) are the same and
wherein the piston rod (20) is rotatable with respect to the housing (4).
