Brain game EUREKA Interlock

Select pieces from INTERLOCK'S complete mathematical set of 12 building blocks to build 50 different shapes. Each 1x1x2 block is numbered and has one plug and one socket in a unique location. You build shapes by fitting each plug into a socket of the next piece. When the puzzle is solved, each plug will fill a socket, and the completed shape will have no plugs or sockets visible.