Insert the FirstScope's metal cylinder screw into the hole of the scope-adap-top.stl part with the plastic and metal washers inserted on the opposite sides.
Place the large knob back on to the metal screw cylinder and tighten to secure it to the 3d printed mounting adapter.
Press the eye piece into the adapter to snap it into place. The iPhone adapter fits best without a case.
The 1.25' standard eye piece is placed into the viewing lens part of the Celestron FirstScope. Tighten the two thumb-screws on the side to secure the eye piece.