Stewart Coffin designed this puzzle in 1990. It is made of ten identical pieces, one key and one augmented piece. Assembling and disassembling the puzzle requires shifting the pieces back and forth in order to insert or remove the next piece. Mr Coffin considers this puzzle to be difficult to solve, (assembly in particular) He considers the 12 Piece Separation one of his top favorite designs.
This 4 color 3D printed version has been made by Lee Krasnow from Pacific Puzzleworks.