A glass rimmer is a bar accessory used to apply salt

Salt

In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...

 or sugar to the rim of a glass. It usually consists of one or more shallow plastic or metal discs that the glass is turned upside down into. The discs can be filled with either the rimming salt or sugar, or sometimes something to moisten the rim of the glass such as lime juice

Lime (fruit)

Lime is a term referring to a number of different citrus fruits, both species and hybrids, which are typically round, green to yellow in color, 3–6 cm in diameter, and containing sour and acidic pulp. Limes are a good source of vitamin C. Limes are often used to accent the flavors of foods and...

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