Item used in pair with the second fitting to create connector. This connector joins 4mm hose , through connector, with another pneumatic hose or device. For example, used with 1/8″ – US will create a connector to link Mancraft Spring Engine and standard HPA Line or pneumatic regulator with female US type fitting. To achieve the same link with Micro HPA line 1/8″ – Micro fitting must be used instead of 1/8″ 1/8″ – US.