Precision Port 4" Flared Speaker Cabinet Port Tube Kit The unique flared-end construction of the Precision Port system enables it to outperform any standard port tube on the market. Conventional tubes suffer from nasty turbulence at the entrance and exit of the port, producing unwanted noise and poor sound quality. The Precision Port system overcomes these problems and as a result can actually produce a gain of up to 3 dB in output! Now you can experience good looks, low distortion, and superior overall sound quality thanks to the Precision Port system. Convenient front screw holes make this tube easier to install than others on the market. Create a port up to 17" long, then glue with ABS glue found at any hardware store. Installation instructions included. Dimensions: 7-1/4" outside flare outer diameter 6-1/4" cutout 6-3/16" inside flare outer diameter. Also available in 2", 3", and 6" diameters. Proudly made in the USA!