Made of solid natural rubber and featuring a low sulfur content, these black stoppers are able to stay pliable over a long period of time. They are ideal for use with both non-aggressive or concentrated solutions. They are capable of withstanding temperatures ranging from -13 to 158F (-25 to 70C). The size of each stopper has been marked on the top in raised figures. The size 16 stopper features a top diameter of 128.07mm, and a point (bottom) diameter of 90.63mm. It is approximately 50.16mm thick. The two holes offset from the middle of the stopper are roughly 5.05mm in diameter, and go all the way through the stopper.