You are bidding on a custom designed, precision machined Arca-Swiss style L-bracket plate for the Nikon D3 or D3s body. It is made by Really Right Stuff in California from a solid block of 6061-T6 aluminum. The model number is BD30L A. The L bracket allows the camera to be quickly changed from vertical to horizontal orientation on the tripod without altering the tripod head adjustment.
It is used and has a few minor surface flaws, but is still a thing of beauty. The design and manufacturing by Really Right Stuff sets the standard for Arca-Swiss compatible gear. It is absolutely just as functional as a brand new one for a fraction of the original price of $183.00