of the insert 14 in the position shown in fig1 the first part of the drive sleeve 60 may be considered as comprising a first portion aligned with a second portion more generally in the position shown in fig1 the first portion of the drive sleeve 60 is located between the insert 14 and the piston rod 32 while the second portion is located between the piston rod 32 and the dose dial sleeve 60 a second end of the piston rod 32 and an internal surface of the drive sleeve 60 are splined together such that no relative rotation may occur between these parts only longitudinal displacement the outer surface of the second portion of the first part of the drive sleeve 60 is provided with a helical thread 62 a nut 64 is provided on the helical thread 62 between the drive sleeve 60 and the dose dial sleeve 50 the dose dial sleeve 50 and the nut 64 are splined together by spline means to prevent relative rotation between the nut 64 and the dose dial sleeve 50 the second part of the drive sleeve 60 is of larger diameter than the first part of the drive sleeve 60 there is a step 66 between the first part of the drive sleeve 60 and the second part the second part of the drive sleeve 60 is seated within the second section of the dose dial sleeve 50 the shoulder 56 of the dose dial sleeve 50 and the step 66 of.