Our knee board is designed to aid in the installation of the vents into an existing floor. Also known as a retro-fit application. The Knee Board is cut from 1/4" steel and powder coated for durability. Each of the two ends of the knee board has a cut out template in the size of your choosing. The template is designed to be used with our 1/2" flush trim router bit with a 1/4" tall cut and a bearing on top. Click Here to view the Router Bit.