The Manfrotto 509PLONG Quick-Release Plate for 509HD Head is an extra-long (5.5") plate for a video camera. It's compatible with the 509HD head as well as other newer Manfrotto video heads.
The plate features 3/8"-16 and 1/4"-20 screws for compatibility with virtually all video cameras, and there's a fixing pin to prevent any twisting. With its built-in index, the 509PLONG plate works with Manfrotto's Advanced Balancing Recorder (ABR) system.
Manfrotto 509PLONG Quick-Release Plate for 509HD Head