These tiny valves are the best
These valves are the best. I tried other inline valves for a higher price and they didn't work as well as these. The incremental dial up or down of the air flow is amazing. They work like a charm.
Airbrush Quick Release Disconnect Coupler & Plug with Airbrush Airflow Adjustment Control Valve (1/8" BSP Male and Female Connections) (Airbrush Not Included)
Fits airbrushes and hoses with 1/8" size fittings, such as Iwata, Devilbiss, Master Airbrush and many other popular brands.