Barrels are one of the most popular kumiki
shapes. These two (the large one has been discontinued) all have the same
numbers of pieces, and are solved the same way. They all come with a solution diagram, are
wrapped in cellophane.
A mechanical puzzle is a self-contained object, composed
of one or more parts, which involves a problem for one person to solve by manipulation
using logic, reasoning, insight, luck, and/or dexterity. - Jerry Slocum