Rubik's Revenge® (4x4) is a limited release upgrade on the world's best selling puzzle - Rubik's Cube® (3x3).NOTICE: The 4x4 and 5x5 are inherently less durable than the 3x3 cube due to the considerable additional moveable parts. While Rubik have endeavoured to, and are confident of, these puzzle being the best quality possible it is only fair to it's customers to be made aware these puzzles are not suitable for 'speed cubing'. These puzzles should not be forced to twist and must be aligned correctly before twisting to prevent damage. As such, we can not be responsible for repacement of 4x4 or 5x5 Cubes which break during use due to turning misaligned rows.