The Number Blocks comprise of Sapele for the box, maple for the pieces and walnut for the digits. Dimensionally it is about 4.5 inches square and 1.5 inches tall. Made by Tom Lensch, the puzzle is of the usual outstanding quality and construction and all the pieces move and slide smoothly.
This is an interlocking "packing puzzle" and the object here is to rearrange the pieces from the start position to the finished position as shown in the photos here. Basically you need to swap the positions of the 3 and the 4 to the right order.
Like most of Goh's designs, there are not many pieces - just 4 ordinary looking blocks adorned with laser cut digits atop each one. But three of these blocks have extensions popping out from their sides and these protrusions interact with a channel cut into and along all four of the insides of the box. They also restrict each other's movements within the box. The solution takes a number of steps more akin to a burr puzzle. Difficult? Well, for the more experienced puzzler, not overly so nor frustrating. But this a puzzle which requires you to exercise some thinking and re-evaluate how you would solve a packing puzzle. And typical of Goh's design style, there is usually a "trick" of sorts to solving the Number Blocks which results in a nice a-ha moment solution.