Additional Weaver rail on the gas block allows you to mount the red-dot scope on your carbine but still be able to shoot using standard iron sight. The rail is secured on the carbine frame by three screws and nuts what ensure stability even after series of shots.
The bore diameter of akm gas block: 19 mm
The bore diameter of saiga gas block: 19 mm
Example of akm and saiga with weaver rail used to mount red-dot scope combined with the magnifier.