I've looked all over the place online, in Canon booklets/instructions, and in the Canon Compendium by Bob Shell. I can't find any information about what this thing is. Any help would be greatly appreciated.
My hope is that it is a useless rangefinder accessory worth thousands of dollars.
Like others I will go with spacer on the bases that I sometimes could use something like that when using a long len with a tripod collar in some cases I have to use the tripod head in reverse otherwise the camera gets in the way.