Reflex port (tube). AZ Audiocomp.

AZ Audiocomp AR 40/D reflex port (tube).

AR tubes are made of PVC and are available in five different sizes for mounting speakers from 10 to 46 cm. diameter. 
They have a rigid edge that permits to easily fix them from outside the enclosure. 
AR tubes are telescopic in order to be suitable to all needs and to allow the reflex perfect alignment without rebuilding the whole system.