Can someone please help me identify this (for me) unknown lens mount? I found it on a Pentacon (Meyer Orestegor) 500/5.6 lens, which originally was sold with either Pentacon 6 or M42 mount, but this is something different.
There is a black tube coming out 5mm from the silver base plate. The tube has an outer diameter of 38mm and an inner diameter of 35mm and is threaded only on the inside. The outer surface of the black tube is plain.
On the base plate, there are three wings in some distance from the tube. As seen on the left side of the second image, the wings are gripping inwards.
Counter-clockwise of one of these wings, there is a small, fixed pin. The pin can be seen on the first image at about 2 o'clock, on the second image at the right hand side.