Once the secondary is safely stowed, the Fastar optics set can be installed in its place.  This optics set, which resembles a large telecompressor, fits tightly in the secondary opening.  My set had such a tight fit I had to lubricate the edge with graphite from a pencil.  Once installed, the secondary retaining ring is placed back over the assembly (seen here just below the orange print) and firmly tightened.