This instructable is about the construction of a dive light with parts that you can get at the local harware store.The ring at the back side is used as a rotary switch. This ring is coverd with ballbearing balls for grip. More details can be found at http://www.divelight.me.pn/ or http://www.duiklamp.me.pn/ for an explanation in Dutch.
Step 1: The parts
Basic parts are a 50mm alluminium tube of 250 mm and a number of PVC "plumbing" parts.