TEC-HRO system bench rest is specially for shooting with a rifle-scope.
One of the black part is before and the other behind the chamber. Also you can adjust the black parts under the silver rail (closer together – and also 4 and 8mm sideways). The rifle-scope will be fixed at the silver rail.
It has a hight of 15mm and can be increased with a special "distance-kit" in 2mm steps till 35 mm.