PTFE Tape (aka Plumber's Tape) is used to wrap around your threaded brass or stainless steel connections. This will provide a tight seal and prevent leaking. Simply wind tape around the cleaned threaded portion clockwise for 5-6 complete rotations. The PTFE will provide the friction needed to align your thermometers and stainless ball valves leak free.
Works for any threaded connections on your keggles or pots, camlocks and other stainless steel brewery items.