Construction arm
A construction arm is an adjustable mechanism in a universal constructor that allows new objects to be constructed in any chosen location that the arm can reach. A construction arm generally consists of a shoulder containing fixed guns or edge shooters, a movable construction elbow that slides forward and backward along the construction lane(s), and in the case of single-arm universal constructors, a hand target object at the construction site that can be progressively modified by a slow salvo to produce each desired object.
The single-channel UC toolkit now includes specialized recipes for such tasks as creating a new hand target starting from just an elbow, efficiently moving either the elbow or the hand forward or backward long distances, building 0-degree or 180-degree glider salvos as well as 90-degree ones, building orthogonal spaceship salvos, and creating and removing lossless 90-degree bends from the construction arm (these last are the Snarkmaker and Snarkbreaker recipes). These can all certainly be useful for completing construction tasks more quickly, but they're not required for construction universality.