NPTF fittings create a mechanical seal when a male and female fitting are mated. The female hose end crushes the thread of the male fitting, creating a tight, robust connection. NPTF fittings are known as "dry seal threads" because they don't require thread sealants, which can dissolve and contaminate fluids or gases in high-temperature and high-pressure applications. NPTF fittings provide a more substantial, leak-free seal, but are more prone to damage from over-tightening and require careful handling during installation.