Auspex Scientific - The Exciting Science and Educational Store
Twist one of the three rubber protrusions off, and the solid stopper becomes a one-hole stopper. Twist another one off, and you have a two-hole stopper. Twist the remaining one off, and it becomes a 3-hole stopper.
Made of "white" natural rubber, with safe, convenient, countersunk 5 mm hole.
Top diameter: 26 mm
Bottom diameter: 23 mm
Height: 25 mm
5 stoppers per pack.