Manfrotto 394 Low Profile Quick Release Adapter with 410PL Plate

When you push on the lever to release the adapter plate there is an edge that is rubbing/pressing against an angled surface on the bottom of the adapter plate (that is secured to the bottom of the camera). When using a new adapter plate there is still paint on that portion of the plate where the lever presses/slides. With use a small area of the adapter plate has the paint worn off and the bare metal presents less friction to the rotating/pressing lever than it did when there was still paint on it. To make it easier to remove a new adapter plate (before a worn spot developes in the paint) observe how the tightening/locking lever works to tighten-down the adapter plate and see where the two surfaces press/slide against each other; then put a tiny dab of petroleum jelly on that area (I then took a tissue paper and rubbed most of the petroleum jelly off - you only want the tinest amount possible to reduce the friction of the sliding metal surfaces without making a mess).

Yes, if you use the 3/8" female by removing the 1/4" adapter from the base.

Three and a quarter inches long by two and one half inches wide.Good sized plate.

bought these to use on camera stands in the studio, and they work extremely well. I am not sure about their compatibility with other tripods.

Yes it is completely flush on the bottom, and given the setup you just described, the release lever would be on the left.

We use it as a quick release for our gimbal attached to our UAS carrying a Cannon 5D Mark III. We also use the same quick release for our DJI Ronin M. It can get difficult to release it if you do not have a lot of space between your gimbal arms and camera body. But it works great for us!

I have multiple copies of this item, they all came with a removable 1/4-20 bushing in the 3/8 thread on the underside.

The quick release system with the plate is approximately 0.75 lbs and without the plate it is approximately 0.53 lbs.