The inner extension is 2.5 cm diametre. Wont conduct electricity up to 240V if not contaminated with moisture, water or other conductive liquids.
The Nylar thread accepts lock clip on Mr LongArm bulb changers to prevent loosening during use. The end thread is typically AMCE or US thread , which is what most people refer to as the thicker thread for paint rollers. This thread is able to be converted to the EURO fine thread which is the same thread as a standard commercial mop handle.