threaded pipe fittings. A threaded pipe has screw-threaded ends for easy assembly. Threaded pipes used in some plumbing projects to carry gases or liquids under pressure feature a tapered, slightly conical thread. Threaded fittings are utilized in non-critical applications and when the service fluid, such as instrument air, plant air, cooling water, potable water, and so on, is at room temperature. They are utilized in situations where welding is not authorized since they do not require welding.