A jigger or measure is a bar tending tool used to measure liquor, which is typically then poured into a cocktail shaker. It is named for the unit of liquid it typically measures, a 1.5 fluid ounce (~44 ml) jigger or shot. However bar jiggers come in other sizes and may not actually measure a fluid jigger.
A traditional style of jigger is made of stainless steel with two opposing cones in an hourglass shape on the end of a rod. Typically, one cone measures a fluid jigger and the other 1.0 fl. oz. (~30 ml) pony (shot) or 0.75 fl. oz (~22 ml). Other combinations include 2 fl. oz./1 fl. oz. and 1.75 fl. oz./0.75 fl. oz. combinations. A typical British "jigger" measures 50ml on the larger side, and 25ml on the smaller side. A variation on the double jigger excludes the rod. In the UK, to double, or sometimes even triple the measurable amount of liquor within a cocktail or mixed alcoholic beverage is known as a Geraghty Measure.