A string puzzle is any mechanical puzzle where the emphasis is on manipulating one or more pieces of string or rope. The string(s) may be closed loops or unclosed or fixed to some given harder material in a certain way. Usually there is only one piece of rope or string. The string may have balls or similar attached to its ends. There may also be a ring or similar sliding along the string. Some pieces of the puzzle may be constructed from various materials such as wood/wire/iron/leather/plastic or other material.