The Grainger Approved 16-004 Stopper is a black rubber stopper with a 16 mm diameter and 90 mm length. It has a solid top and hollow bottom to fit various sized containers and test tubes. The stopper is made from high quality SBR rubber that resists cracking and provides an airtight seal. It can withstand temperatures from -20°F to 250°F. The stopper meets ASTM D3574 standards for rubber stoppers. It comes individually packaged. This basic rubber stopper is suitable for home, school, industrial, and laboratory use.