NPT fittings, or National Pipe Tapered fittings, are a type of threaded connection used in plumbing and piping systems. They feature a tapered thread design that allows for a tight seal when two fittings are screwed together. This design helps prevent leaks and is commonly used in various applications, including water, gas, and air systems. These fittings come in various materials, such as brass, stainless steel, and plastic, making them suitable for different environments and pressures. Proper installation is crucial, as over-tightening can damage the threads, while under-tightening may lead to leaks.