Brass Plated Extensions.....Smooth Brass plated lamp pipe extensions with threads at top and bottom. 3/8 inch diameter (OD) 1/8 IP. You can run lamp wire through these pipes. ( 1/8 IP is an industry classification ), if you want this pipe to pass through wood, you must drill a hole slightly larger than 3/8 ( say 7/16").Fasten with lamp washers and pipe nuts.