This is the Harder And Steenbeck 125903 3m Braided Hose (1/4in - 1/8in).

Specifications:
Length: 3 meters
Compressor End (Female Thread): 1/4"
Airbrush End: NW 2.7mm Quick Connector Compatible with Harder & Steenbeck Airbrush Ferrules
Hose Diameter: 3.3 x 7 mm
Part Number: 125903
Made in Germany