The cube is of a solid piece of 6061-T6 Aluminum (more commonly known as “aircraft grade” aluminum). The exterior measures 1.9″.

From CNC Cookbook:
The Turner’s Cube is a fascinating object. In the old days, novice machinists were handed one and told to work out how to make one of their own. It was considered a good test to give a budding machinist to see whether they could first understand how to go about making one and second to see whether they could operate the machinery to the level of precision needed to produce a nice cube.