Even when no chain or cord is included, often there is a hole or a loop where one could be attached.
In this section, I have focused on the interlocking variety of keychain puzzles though I do show some other types I've collected.
Collector Steve Butler has written a couple of articles on keychain puzzles - one article entitled "It's a Puzzle" appeared in the September/October 1991 issue of The Toy Collector magazine.
Another two-part article "Key Chain Puzzles" appeared in Antique Toy World in April and May 2004.
In 2011, Jerry Slocum and William Waite issued their Compendium of Keychain Puzzles, which gives details for 465 puzzles (467 according to the internal numbering but there are unassigned numbers).
Several interesting designs were issued in France, Japan, and others in eastern Europe.
Several from the 2011 1st edition have been reclassified or renamed, or dropped as it was decided they don't really qualify well. know as "keychain puzzles" are known as "Jig Toys" and have been issued as cereal box premiums.
Unfortunately the assigned numbers have changed from the 1st to the 2nd edition. I like the idea of thinking about these puzzles as miniature "jigsaw toys" - the best designs seem to me, while not exactly having the traditional curvy tabs and notches of a jigsaw, to have pieces that interlock along non-obvious borders. That site has nice pages about Jig Toys free in Corn Flakes in 1959, in Sugar Smacks in 1960, in Frosties in 1960, and in Frosties in 1970.
Most collectors of keychain puzzles will admit certain small interlocking constructions into their collections even when the puzzles were not really intended to be hung on a keychain - I have included some examples here.
They are referred to as "Miniature Plastic Interlocking Puzzles" and many were produced in Japan.
But of course part of the fun of collecting is to define one's own boundaries.