This is my design to mount a E27 lamp to a piston and connecting rod from an Mercedes V8- Engine. The outer diameter of the adapter is 50,2mm and the inner diameter is 37,4mm. You'll need to print this 2 times and depending on your printer you might have to sand the ends a bit to make it fit. Feel free to customize the .step file to fit other pistons and/or lamps, tagging the original will be much appreciated.