Fourth hose enables connection to HI/LO sides, refrigerant tank, and recovery unit or vacuum pump for diagnostics. evacuation and charging without switching hoses - 1/4" hi/lo sides with 3/8" vacuum port for regular jobs - 3/8" hi/lo sides with l/2" vacuum port for larger systems Front access for easy field recalibration Proven, double "O"-ring piston for reliability and long service life Exclusive lOO-mesh filter in-line on all flare fittings helps keep out particulate material and extend the life of the seat Contoured easy-grip handles for positive control; color coded for ready identification Sight glass to easily view refrigerant movement and condition during charging and recovery Heavy-duty hook won't pull out Also available with LAX) 3-1/8" (80 mm) red and blue liquid- filled gauges