Item used in pair with the second fitting to create connector. It joins 4mm pneumatic tube, through connector, with another pneumatic tube or device. For example, used with T type fitting 1/8″ [Female] – 1/8″ [Female] – 1/8″ [Female] will create a connector to link Mancraft SDiK Engine and other devices connected to the T type fitting, like pistols or secondary guns or 1/8″-US [Female] fitting for HPA lines.