Brilliant piece of kit that entirely replaces the quick release platform with an Arca Swiss quick release on the Manfrotto 405/410 geared heads. What's a geared head? It's basically a head where the adjustments in 3 planes are adjust by gears - you simply turn each of the 3 knobs to achieve the perfect composition, making it the ideal for macro, landscape and architecture. No need to worry about locking off the head like you would with a ball head, just dial it in precisely where you need it.
Unfortunately geared heads tend to be bulky and expensive, and even the most economic model, the Manfrotto 410 'junior' geared head (which I use) has an enormous quick release plate (designed for medium/large format cameras) that gets in the way even on a pro-sized DSLR and looks ridiculous.
Up until now, I've used a Kirk Arca-Swiss style plate on the camera and a Kirk QR platform bolted onto the Manfrotto plate - a bit of a kludge to say the least, and I've always fretted that I'd accidently release the Manfrotto QR and see the whole lot tumble to the floor, or that the Kirk QR platform would simply twisting off, being attached by a single 3/8" bolt.
Enter the innovative Hejnar Photo adapter, essentially a precision machined plate that replaces both the Manfrotto plate and the Manfrotto QR platform, bolting instead directly to the head. A Hejnar Arca Swiss QR clamp is then attached to the plate by 3 bolts. You do need to disassemble and remove the Manfrotto QR mechanism, but the result looks neat and feels a good deal more secure.
I assembled mine with a little thread-lock, but since the attachments (head-to-plate and plate-to-clamp) are by 2 and 3 bolts respectively, there's no real possibility of either twisting off. Available from Hejnar Photo ebay store here, and if you prefer to use a different clamp, the adapter plate is available on it's own.
As supplied, there are a couple of minor downsides: firstly the supplied clamp is a little wider than the plate and partially obscures the bubble level on the 410 head - but then again this is totally obscured once a camera is mounted; and, when the camera is in portrait mode, it is impossible to tilt the camera up or down, making composition tricky. Fortunately, both problems can be completely resolved by simply unbolting the QR platform and swinging it through 90 degrees - tapped holes are provided for either orientation.
Overall this is an excellent niche product that solves a tricky problem for those that want to use a geared head with DSLR cameras.