Here I copied that profile from the lens cap to create the internal thread:
Once I put the pieces together, I used section view in order to see the internal parts for mating them up. The parts that I built for this project (all shown except the lens which was suppressed during the bulb mating), include the housing, lens and lens cap, o-ring, bulb, switch, battery and battery cap.
All together now:
I want to click the switch.