[Disclaimer] I've personally helped to provide input on the design of this particular product along with PhotographyandCinema.com. I find this small item incredibly useful, but please make your decisions based solely on the product functionality and not my personal opinion.
The Common Problem
The Manfrotto 501PL Quick Release plate is compatible across several of Manfrotto's Video Fluid Heads making it highly popular among DSLR Video Shooters. The 501PL (or compatible) quick release plate offers an anti-twist register pin, but the design of DSLR camera bodies are unable to take advantage of this.
An Innovative Solution
For this widely common problem, PhotographyandCinema.com has exclusively designed this special ATP adapter kit that will transform ordinary 501PL plates into an anti-twist plate specifically for popular DSLR cameras or smaller Interchangeable Lens (ILC) Camera bodies. The ATP is designed to 'LOCK' in place above the 501PL plate and adds an anti-twist lip across the camera body.
Using the ATP Plates WILL NOT CHANGE the basic functionality of your 501PL plates when moving from your favorite tripod heads (like 701HDV), favorite monopods (like 561BHDV), and to 501PL quick release adapters. It is designed to enhance the abilities of your 501PL plates when working with DSLR Video cameras.
The ATP Plate is not at all required when working with DSLR Video, but it will help to eliminate the annoyance of cameras shifting over the 501PL. For some that's a small price to pay for peace of mind when working on important projects. Pricing has not yet been announced, but more information about the ATP Plates and a 20% OFF Coupon (when available) can be found at the product page at http://PhotographyandCinema.com.
(Above) Example shown with 5D Mark II, Panasonic GH2, Nikon D600