This useful item allows you to align the laser beam. It is a thread insert with a pair of copper wires and can therefore be screwed in at any location between parts to check for a central beam. Once the beam is aligned, replace it with a normal thread insert. A quick beam burn on card or viewing the beam on a mode plate will show the silhouette of the wires.
Make adjustments until the silhouette cross is central to the beam. You need to check the alignment a various places, working your way from the laser to the work piece. Any odd mode pattern may indicate that the beam is reflecting off the inside of a pipe or is being clipped somewhere.