Here's a cool little item shared by HDSLRNOW.com that mounts a set of 15mm rails and allows you to adjust the rails up/down/left/right. The purpose it help line up accessories that might otherwise be offset as a MatteBox in the example below. [Thanks Joel]
Best part about this post thanks to HDSLRNOW.com is the item is being offered for $0 dollars, a limited amount is FREE. Check it out over at the CoolRaiser product page (Click Here).
CoolRaiser 15mm Adjustable Dual Rail Clamp
For more helpful tips on gear like this, visit HDSLRNOW.com