A 4-inch snap collar is a circular fitting designed to be mounted onto ducts, pipes, or walls to create a clean, secure transition point for round ducts or flex pipes. The "4-inch" refers to the inner diameter of the collar, which matches standard 4-inch ducting.

It typically features a snap-in flange that locks into place, making it easy to install without screws or welding. It can be used for ventilation systems, dryer exhausts, HVAC applications, or dust collection systems.