Summary: Fits perfectly on my D7000. Allows the camera to slip on round eyecups and makes the viewfinder more comfortable when holding the camera in portrait. Round eyecup covers eye perfect and allows very little stray light in. Also gives the camera a very professional look and feel. Great purchase. Get it! then get a round rubber eye cup to go with it.
Summary: I have had a 'love affair' with the Nikon SLR system for over 40 years but even Nikon doesn't always get everything right! Here I'm thinking of their early ventures into auto-focus with the F501 body which was my first experience of a rectangular viewfinder. This came with a nasty piece of plastic (DK-5) which could be threaded onto the camera strap and was provided to blank off the rectangular eyepiece when necessary.