These are used in air brake systems that are serviced by SAE J844 nylon tubing.
DOT applications require that the fittings be marked with DOT on them.
Male connector
Size 1/2″ tubing o.d., 3/8″ male pipe
Nylon air brake fitting Meets DOT FVSS571.106 air brake specifications. These are used in air brake systems that are serviced by SAE J844 nylon tubing. D