A spindle for driving a bung of a cartridge. The spindle includes a generally circular shaft having an outer surface. The generally circular shaft extends from a distal end to a proximal end of said circular shaft. A first helical groove is provided along a first portion of the outer surface. The first helical groove having a first pitch. A second helical groove provided along a second portion of the outer surface of the generally circular shaft. The second helical groove overlapping the first helical groove. The second helical groove having a second pitch.
