The ZKK peep sight is a very nicely designed and engineered unit, quite complex machining required for all the parts and particularly the recess cut into in the rear receiver bridge.
I know, because I have 3D CAD modelled most of the parts

It folds flat level with the top of the receiver and was designed to be used with the QD Zeiss Jena scope but other QD rings like Alaska Arms will also work fine.

They are adjustable for both elevation (via the front screw) and windage (later peeps had a dovetailed friction fit with reference lines, early pre-68 versions also had a lock screw).

See my ZKK 600 and 601 below:

The CZ USA Custom Shop at one time offered them installed and fitted on a CZ 550 Magnum for $330: