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Pressure fittings are available in a wide variety of sizes and configurations. The most commonly used connection in North America is the "National Pipe Thread" (NPT), which creates a seal by the intermeshing of the threads along a tapered thread line. Since this method can still allow a leak path between the thread crests and roots, the application of a thread sealer is required, in the form of Teflon® tape or a hardening liquid chemical compound referred to as "pipe dope". However, process interface requirements, dynamic forces and differing international standards often preclude the use of NPT fittings in favor of more sophisticated pressure connections. Among the various alternatives are fittings that form the pressure seal through the use of an O-ring, gasket or metal-to-metal compression assembly. But despite the many application-specific connection requirements, the most compelling divergence from NPT is the need to contain higher pressures.