Abstract: This invention is a teaching aid for use by children and others in learning the association between mechanical items. It is characterized by two parts of a mechanical item which are capable of being connected together, being respectively connected to different portions of pieces of a jigsaw puzzle-type apparatus in such manner that when the jigsaw puzzle is correctly assembled, the matching mechanical elements will be in a position to be joined together, and in such manner that when all such items are correctly joined together the jigsaw puzzle will remain in an assembled configuration until the elements are disconnected.