My buddy has a JessEm Rout-R Lift II he uses as part of his woodworking shop. I designed this customizable insert ring in OpenSCAD so he could print off whatever size he needs instead of having to purchase them. Pictured is an original ring (red) beside a printed one (black). Perhaps this will work in other manufacturer's router lifts and tables, perhaps not. Feel free to rework my .scad as needed for your purposes.