The Puzzle

a.k.a. Double Cross
Made in Japan, circa 1930?, level 1, no holes.
(six wood pieces, each 5/16 inches square by 2.4 inches long)

Another example of a Simple 6-piece Burr. Also in the theme of pages 106 and 139-140 of the 1983 Hoffmann book, but also simpler. Two identical pieces form an empty rectangle, a double notched piece goes in the bottom, two identical pieces go on each side, and the key piece slides in:

Double Cross (another example of The Puzzle)

Old design, level 1, no holes, notchable., circa 1960s-1980s??
(six aluminum pieces in a cardboard box, 2+3/8" x 2+3/8" x 1/2";
directions on the back of the box are shown above)