The Iwata Pistol-Grip Filter is a filter that is inserted between the airbrush gun and the hose. Collects condensate formed from the compressor and allows your airbrush to feed clean and dry air.
Provides a good flow and prevents a variety of nuisances that moisture can cause in your airbrush pistol. If your compressor already has a similar filter, it's still good to use the Pistol-Grip Filter too, as the condensation can still arise in the hose from the air comming from the compressor to the gun.