all of my Technika 4x5 boards have a raised circle about 3/16 " diameter at the back, at the top. What purpose does it serve? It causes no problems on my Technika IV, however with my Kardan conversion board, the Technika boards do not lie completely flat. This has not been a problem so far. I have a device that allows Technika boards to be used on a Fuji GX680, this however leaves a gap that will most certainly cause problems - I intend to make an appropriate size depression in this device but have not figure out how, as yet.