An assembly nest for transporting a tubular sub assembly of a drug delivery device on an automated production line, in which the tubular sub assembly includes a tubular body and a cap that is wider than the tubular body. The assembly nest includes a base against which a sub assembly of a drug delivery device is mountable to orientate said sub assembly in a predetermined position； and locking mechanism having a resilient member to urge the locking mechanism into one of: an unlocked position, in which a sub assembly of a drug delivery device can be mounted to the base； or a locked position, in which the locking mechanism engages a mounted sub assembly to retain it in its predetermined position on the base.
