5.5mm Solid Carbide 4 Flute Double Angle Internal Cutter 60° & 45°, Kopp Germany
Made by Kopp Schleiftechnik in Germany. 2nd to last photo is the actual product spec from Kopp that was in the box. (in german.). You won’t find this cutter in their catalog since its a custom job. Rear Angle = 45 Degrees.