The coil head is the part usually with holes in the side that threads down into the base - the base is the part that threads down onto the device itself. Uno momento - I'll get photos pf a common coil head (in todays standards):
From Left to right: Drip Top, Top Cap, Glass Tank Section, Coil Head, & Base. The coil head usually screws into the base and sometimes the pin on the very bottom of the head (the metal just below the white ring) itself needs to be adjusted. No worries though.