[Jonathan Moore]

Basically there's a main casting, of course mines a fabrication.

The casting is attached to a top plate that slides into the location rails and is attached to the vision hole blanking block via a threaded bar.

In the location rail there are two location holes, one positioned so that when the periscope is not required the blanking block covers the vision holes and one that aligns the periscope with the vision holes. To release the assembly, so that it can be slid one way or the other, you press the lever on the side of the casting in, this lowers a sprung loaded plunger. The assembly can then be slid across and the plunger will then locate into the relevant hole.

Because our eyes are not the same distance apart, person to person, there is an adjuster that would allow the vision tubes to be adjusted to suit the user. This is attached to the lower part of the casting and contains a thumb screw attached to a threaded bar, one end is threaded with a left hand thread and the other with a right hand thread.
If the thumb screw is turned one way the adjusters move apart, if turned in the opposite direction, the adjusters move closer and when the vision tubes are assembled into the casting, this adjusts the distance between the eye pieces.