Welcome to Interlock, the hide the plug and socket puzzle! 

The Goal: Select pieces from Interlock's complete mathematical set of 12 building blocks to build different shapes. Each 1 x 1 x 2 block 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. 

The Challenges: There are 50 shapes to build arranged easy to hard. Each challenge illustration lists the number of pieces needed to make the shape and the number of possible solutions. If you get stuck, we provide a multi-part hint for each challenge. It lists the pieces needed to complete one possible solution, shows you the orientation (piece outline) for the pieces and the location of several puzzle pieces within the shape. If your plugs and sockets aren't connecting, a complete solution for each challenge is provided. It lists a numbered assembly sequence and shows a diagram locating all the pieces.