An assembly for the administration of a selected dosage of insulin or other medicaments from a cartridge by moving a plug guided in said cartridge, comprises an adapter assembly for adapting cartridges with different dimensions or contents. The adapter assembly comprises a first threaded element threaded with a thread lead and movable in a moving direction to move the plug, and a second threaded element threaded with a thread lead for setting a selected dosage, pivotably screwed to said first threaded element and limiting the movement of said first threaded element, and wherein said thread lead of said first element and said thread lead of said second threaded element are adapted to the dimensions and/or the contents of said cartridge.
