In mechanics, an air collar is a device that is used to control the flow of air in a system. It typically consists of a collar-shaped object that is fitted around a pipe or duct, and can be adjusted to increase or decrease the amount of air flow through the system. Air collars are commonly used in heating, ventilation, and air conditioning (HVAC) systems, where they can be used to balance the flow of air to different parts of a building or to control the temperature in specific areas. They can also be used in other types of mechanical systems where the flow of air or gas needs to be regulated.