The goal of the puzzle is to fit the four T shaped blocks into the box, with the pieces flat. The box itself has two sides so there are two versions to fit the pieces. The first side has a larger area so it is pretty easy to fit all the pieces into the space. This side of the box has multiple solutions. Next, you flip the box over and the sides are thicker, giving you less area to place the T pieces. Notice that the previous solutions don't fit anymore. The actual solution requires a unique pattern for the T pieces to work.

I understand the inventor of this puzzle is Peter Haject and multiple versions (wood and plastic) with different shapes/sizes are spread across the web. I felt like this version was pretty easy to make but if you are not up to it, feel to purchase a similar version from online.

This video shows the solution. Skip it and don't go past Step 10 if you want to try to figure it out on your own.

Step 1: Tools/Materials

Tools:

Table Saw
Router / Table
Ruler or Calipers
Pencil
Sander
Wood clamps

Materials:

Wood: 1.5" x 24" x 1/2" thick
Wood: 3.5" x 3.5" x 5/16" thick
Wood glue
Paint/Stain (optional)

Step 2: T Build

Start by cutting a strip of wood to 1/2" x 1/2" x 24" long. You don't need 24" but the extra length allows for a few extra Ts which is a good thing if you are known to mess up like me.

Step 3: T Parts

You will need 4 of each of these pieces. Hold off on the rounds for now.

Step 4: T Assembly

I glued the Ts together. For centering, I used a few of the extra parts (shorter pieces). Again, you might want to hold off on rounding the edges until the final fit check.

Step 5: Box Floor

I used a table saw for all straight cuts.

Step 6: Box Sides

Cut a 1/2" thick board down 1.5" wide. I used a router to cut the rabbet joint.

Step 7: Box Sides

Similar to the other sides except more passes on the router.

Step 8: Ready for Assembly

Step 9: Glue

I used wood glue and clamps to secure the sides and floor. Break sharp edges and clean up with sanding.

Step 10: Can You Figure It Out?

With the dimensions shown for the T (Step 4) and the dimensions shown here, can you figure out a layout that works?

Step 11: Cover (optional)

This part is optional. I didn't make it but it helps with storage.

Step 12: Puzzle Patterns

Ok, here is the solution. The first picture shows one example of how to fit the Ts into the larger box. The second picture shows the optimized placement for the smaller box. You might have noticed that the parts still don't fit into the dimensions shown in Step 10. The key is shown in the next step.

Step 13: Ts in Box

As you can see in the first pictures, the Ts easy fit into the box. I modeled a 1/16" gap on all sides for this layout. For the second version, rotation is the the key to making the pattern fit into the box. Also, rounded corners on the Ts help if your dimensions are a little off.