Take the base off the lamp and keep the screws. Insert the goose-neck base into the printed clip and screw it down using the original screws. Push the clip down into the end of the 8020. Easy!
Printed with ABS, 0.25mm first layer, 0.2mm remaining layers. 30% infill. There are two versions- one for real 8020 (grooves in surface of extrusion) and the other for similar product that has smooth surface. The only difference is a small change in the diameter of the four legs that insert into the 8020.