The present invention relates to an assembly kit for preparing of a pre-filled syringe and in particular to a method of preparing of such pre-filled syringe assemblies by means of an assembly kit, wherein the assembly kit comprises: a gripping means to be attached to a proximal end section of a cartridge which comprises an axially displaceable bung for sealing of an interior volume of the cartridge being pre-filled with an injectable medicinal product, a needle mount to be attached to a distal end section of the cartridge and providing a mount for a needle assembly to be coupled to the interior volume of the cartridge in a fluid-transferring way, a plunger rod connectable with the bung of the cartridge for applying distally directed thrust to the bung, wherein the cartridge is at least partially embedded in a protecting sleeve.
