This Double Cross clone is 19 mm at the base, flaring out to 22 mm and features a 510 connector and drip tip slot. You can spin the golden center ring up for maximum airflow, or close it off completely to prevent leaking when it is laying on its side. The double cross has cyclops airflow holes and nice cyclops-like holes in the three posts which makes rebuilding very easy. The bottom is stamped with a serial number and the crescent moon logo.