The Offset Raised Railblock is essential while building a shoulder rig in which you need to place the dslr body right in front of your face for use with an LCD Loupe like the Z-Finder or the DigiFinder.
The Offset Straight Rail block v2 is essential while building a shoulder rig in which you need to place the dslr body with a Battery Grip right in front of your face.
The Rail Block v2 will let you put together a simple rods support on the DSLR Cage. It will also work in assembling a full rig and will let you mount all your accessories to your setup. It includes a 1/4-20 threaded screw with a wingnut for tightening.