99% sure NPT plug would be the wrong thread. A flare plug might be NPS (national pipe straight). NAPA probably would have some flare plugs.The plugs I normally see for things like that do not have any flare on the bottom, they are just pipe plugs, usually with Teflon tape on the threads. Not arguing the point but just saying that I haven't seen any plugs with a flared end.
99% sure NPT plug would be the wrong thread. A flare plug might be NPS (national pipe straight). NAPA probably would have some flare plugs.