A jigger or measure is a bartending 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 jigger or shot, which measures 1.5 US fluid ounces (44 ml). 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 unequal sized opposing cones in an hourglass shape on the end of a rod. Typically, one cone measures a regulation single shot, and the other some fraction or multiple – with the actual sizes depending on local laws and customs.