Holder is for 1 3/8″ X 3 1/2″ rectangle vents.  The vent is designed to mount under the dash or on the kick panel. The holder measures 6 3/8″ across the top and 1 3/4″ tall. The holder is made of injected molded ABS plastic. The holder works with vents #5014, #5015, #5017 which are sold separately.