Rubber stoppers help contain liquids in test tubes.
Rubber stoppers are the modern equivalent of a cork. Stoppers are used in the fields of chemistry and medicine to help contain vacuums, liquids or gasses in test tubes and flasks during storage and transportation, and are available in several styles. The basic stopper is solid just like a cork. Rubber stoppers are also available with one or two holes bored through the top. Medical stoppers often have a thin resealable top that allows a needle to be inserted.
Stopper Uses
Solid stoppers are used to prevent spilling when transporting or storing chemicals and medical samples. Blood samples are often collected in a test tube with a vacuum inside. A special stopper maintains the vacuum until the blood is introduced via a needle, which is inserted through the thin topped stopper.
Stoppers with holes can have a lubricated glass tube inserted and be fitted with flexible tubing that can be used to connect a test tube or flask to a larger apparatus and still contain the contents such as a gas in a distillation process.
Rubber Stopper Sizes
Because rubber stoppers are tapered, it is a bit difficult to know which end to measure so they are numbered. A small stopper that measures 10 mm on one end and 15 mm on the other is a number 00. The next size bigger is a number 0, and it measures 13 to 17 mm. Number 1 stoppers measure 14 to 19 mm. A number 2 stopper measures 16 to 20 mm, while a number 3 stopper measures 18 to 24 mm. A number 4 stopper measures 20 to 26 mm. Flasks may need larger stoppers. A number 5 stopper measures 23 to 27 mm. A number 6 stopper is 26 to 32 mm. Number 8 stoppers are 33 to 41 mm, and a number 10 stopper, which is 42 to 50 mm, will fit many vacuum bottles.
Cork Sizes
Standard corks are often measured in inches rather than millimeters, so the cork numbers are not the same as rubber stopper numbers. For instance, a number 2 cork measures three-eighths of an inch on the bottom and one-half inch on the top, compared to 16 to 20 mm for a rubber stopper.
Stopper Holes
If you have a solid stopper but need one with a hole bored through, it you can get a stopper borer, also called a cork borer, that will allow you to make smooth holes in your stopper. Stopper borers are available in various sizes based on the diameter of the hole you desire including 5, 7 and 15 mm.
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