The airsoft air seal nozzle, or ASN, is a small hollow tubular part that slips over the cylinder head’s shaft and provides a movable extension that directs air in a compression cycle directly behind BBs as they are loaded into the hop-up chamber.
Air seal nozzles come in different lengths depending on the design of the airsoft electric gun and choosing the right length is paramount to ensure one less source of feeding problems. Too short and BBs might not load into the hop-up chamber properly and you end up with an air leak. Too long and you may prevent BBs from ever loading at all. In addition, the air seal nozzle is usually one of the first components to be swapped out for one that features a rubber o-ring to achieve an airtight seal.