Old design, level 1, no holes, notchable.
(six wood pieces, 3 inches)
The basic idea of level 1 with a key piece is described on pages 106 and 139-140 of the 1983 Hoffmann book. This one is even simpler. Pieces 1, 2, and 3 are identical, pieces 4 and 5 are identical, and piece 6 is a simple solid "key" piece that comes out first.
1.  |
2.  |
3.  |
4.  |
5.  |
6.  |
Assembly:
1. Place pieces 1 and 2 together to form an empty rectangle shape.
2. Lay piece 3 in the bottom of the empty rectangle.
3. Place pieces 4 and 5 on either side.
4. Slide in piece 6.
