Burr puzzles are interlocking puzzles known in Europe and Asia since at least the 18th century. Traditionally they are made from wood

Wood

Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

, but some modern versions use plastic (for reasons of economy) while those of collector's

Collecting

The hobby of collecting includes seeking, locating, acquiring, organizing, cataloging, displaying, storing, and maintaining whatever items are of interest to the individual collector. Some collectors are generalists, accumulating merchandise, or stamps from all countries of the world...

 quality may be made from brass. The wooden burr puzzles are usually precision-made for tight fit and require special wood so that the pieces do not change shape too much in changing temperature and humidity.

The burr puzzle gets its name from the most traditional shape for the finished puzzle, a symmetrical arrangement of intersecting cuboids thought to resemble a seed burr

Burr (fruit)

A bur is a seed or dry fruit in which the seeds bear hooks or teeth which attach themselves to fur or clothing of passing animals or people. The hooks or teeth can be irritants and very hard to get off of clothing, such as wool or cotton...

, but similar puzzles can have other forms: a ball, a human figure, a ship, a bird or a star-like shape.

The mathematical properties of burr puzzles have been studied by Bill Cutler

Bill Cutler

William H. Cutler is a retired American mathematician and systems analyst, living in Illinois USA.His main interest and area of research is in burr puzzles and packing puzzles...

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