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.
This product is designed to be used with DSLRs with battery grips or tall bodies like the 1Dmk4, it helps you mount rods on these types of configurations at the proper industry standard height of 85mm from center of lens to center of rods.