These were made popular by Martinka and Zauber Klingl. Well known German Zaubertechnik Haug had a very successful version as well.
You show two nested boxes with 4 blocks. While magician facing away, ask the spectator to arrange the blocks in any order in the inner box. Then place the smaller box inside the larger and close them up. On your return without opening either box or any funny moves you can discern the exact order of the blocks. The inner box itself is opaque and there is no way you can see inside, but when placed inside the larger box this puts it into the miracle class!
Very good quality magic product!
Outer Box: approx. 6.4″ x 3″ x 1.8″