Here is the first version of a cap I made. It fits over a 1.5" wood dowel that holds light strings across my patio. The inside has a ledge at 40mm that rests on the dowel. This allows the light string wires to be elevated higher then the length of the dowel, in this case about an extra 50mm. The base which is made of light weight concrete also raises the dowel, combined we can get an extra 15cm of elevation.