The positions of the fittings can be obtained by measuring the distance between the centres of the holes in the panels. The use of a spirit level is advisable to ensure panels are level.
Secure the brass ferrel (A) to the wall/ panel with a suitable screw, fig 1.
Screw and tighten the barrel (B) on to the brass ferrel, fig 2.
Align panel with barrel and secure into position with cap (C), fig 3.