Drive mechanisms suitable for use in drug delivery devices

An assembly for use in a drug delivery device comprising a drive mechanism including:

• a housing;
• a dose dial sleeve having a helical thread of a first lead;
• and
• a two-part piston rod;
• characterised in that the two-part piston rod comprises an outer part having a helical thread of a second lead and an inner part having a helical thread of a third lead, whereby the first lead of the thread of the dose dial sleeve is equal to the sum of the second lead of the thread of the outer part of the piston rod and the third lead of the thread of the inner part of the piston rod.

A drug delivery device comprising a drive mechanism comprising:

• a housing;
• a dose dial sleeve having a helical thread of a first lead;
• and
• a two-part piston rod;
• characterised in that the two-part piston rod comprises an outer part having a helical thread of a second lead and an inner part having a helical thread of a third lead, whereby the first lead of the thread of the dose dial sleeve is equal to the sum of the second lead of the thread of the outer part of the piston rod and the third lead of the thread of the inner part of the piston rod.

A drug delivery device comprising an assembly, the assembly including a drive mechanism including:

• a housing;
• a dose dial sleeve having a helical thread of a first lead;
• and
• a two-part piston rod;
• characterised in that the two-part piston rod comprises an outer part having a helical thread of a second lead and an inner part having a helical thread of a third lead, whereby the first lead of the thread of the dose dial sleeve is equal to the sum of the second lead of the thread of the outer part of the piston rod and the third lead of the thread of the inner part of the piston rod.