I ordered these for a demonstration in science class. They are very small - smaller than I thought. They do an excellent job of density work with a small group of students. But you can't really hold them in front of the class.
Pros
Set of 4 specific gravity metal cylinders. The set includes aluminium, zinc, copper and steel. Each cylinder is 1.5" (38mm) long and 0.4" (10mm) in diameter.