The puzzle is to separate the two interlocked keys then join them back together again.
This puzzle was first patented in U.S.A. in 1892 by H.L.Davis. By 1895 it had already spread to the UK and was being sold on the streets of London. It's been a popular one ever since being made under many different names like Puzzle Keys, Magic Keys, The Key Puzzle and even Max and Fritz puzzle. Historical information courtesy J.Slocum & J.Botermans published in "Puzzles Old and New" (c)1986.
Size: The length of each key is 55mm. Presented on a red card inside a window faced brown card box (75mm x 115mm x 45mm) with solution enclosed.