TruThread P NPSM
Thread plug gauge NPSM

ASME B1.20.1
NPSM threads (National Pipe Straight Mechanical) are straight pipe threads used in non-sealing connections. They do not provide a pressure-tight seal on their own but require a separate seal, such as an O-ring or sealing compound, to achieve a leak-free connection.
Unlike NPT and NPTF threads, NPSM threads are not tapered but cylindrical, making them compatible with other straight-threaded fittings. These threads are commonly used in low-pressure applications such as hydraulic systems, ventilation, and industrial hose connections.