This simple little tool takes the guess-work out of figuring out which stopper to use for that flask. Determines the correct size of the cork or stopper needed for any flask, bottle, vial, etc. Simply insert the thin triangular gauge into the vessel and the correct stopper size is read at the top of the neck. Two scales are provided: one for vinyl and rubber stoppers and one for corks. The back side is a circular scale to size tubing outside diameters between 4 and 52mm.