The Manfrotto 577 Quick Release Adapter w/ Sliding Plate is compatible with the 501PL camera plate (supplied with the head 501HDV, 503 and 519 Video Heads) and the special 501PLONG accessory plate. This Quick Release adapter gives you the freedom to remove the camera from the head without detaching it from the plate and put it on any other support. Supplied with 1/4'' and 3/8'' camera screws.
I needed a quick release plate for my glidecam and this does the job just fine
Does its job... averagely
Build quality is great, but the little slip prevention button always gets stuck when putting the plate on. Kind of annoying but I needed a solid mount and this digs job.