A. No, you definitely should not. PTFE tape and pipe joint compound (also known as "pipe dope") should only be used on "IPS" ("iron pipe size") threads, which are normal pipe threads. IPS threads make their seal along the threads themselves; when a piece of IPS-threaded pipe is screwed into a fitting, PTFE tape and/or pipe dope is used to assist that seal on the threads. Flare fittings, on the other hand, seal on the beveled ends of the fittings, and so using pipe dope or tape on flare threads could actually prevent the fittings from making an adequate seal.