It's a flash bracket, just to get ahead of the obvious question. It's designed to clip onto an Arca plate, and the adjustable mount lets you position a remote flash in one of four positions around the barrel of a lens. The tilting flash mount is meant to accept a radio or wired flash remote receiver (like a SC-29 or similar) with its 1/4" thread. It's beautifully machined, of course, from solid, well-finished metal, and while this is obviously a limited-application tool, it won't disappoint when you put it to work.