Tungsten alloy sphere is 2.175" diameter, 1.5kg/3.31lbs. Aluminum is 0.25kg/0.54lbs. Tungsten is a high density element and surprisingly heavy when compared to the aluminum. The set is a great conversation piece. Includes certificate of chemical composition and interesting tungsten facts. Machined from aerospace grade tungsten and precipitation-hardened aluminum alloy, these spheres are an excellent contemporary addition for your desk at work or side table at home. Surprise your colleagues and friends with the spheres' differences Tungsten is one of the densest naturally occurring elements, and now you can add one of nature's wonders to your own collection. If you like the sphere,s don't forget to check out our Tungsten and Aluminum Cube Sets.