Honeywell R-518-CL12-HTG 1" NPT locking coupler with high temp

This article is a locking coupler with a 1" NPT thread, designed for high-temperature service. It is listed under sensor components, indicating that such couplers are typically used to secure temperature sensing probes, thermowells, or capillary tubes in boiler and burner systems where the connection point is exposed to elevated temperatures. A locking coupler provides a positive mechanical connection that resists vibration and loosening, which is important when the sensor must maintain reliable contact with the measured medium. Parts of this type are selected primarily by thread size, temperature rating, and material compatibility. For a 1" NPT locking coupler, the connection must match the mating thread on the boiler manifold, heat exchanger, or thermowell. The high-temperature designation means the coupler can withstand continuous exposure to the temperatures found in flow and return lines, and near the combustion chamber. When replacing such a coupler, ensure that the thread type (NPT) and size are identical, and that the temperature rating meets or exceeds the application's maximum operating temperature. Also check that the coupler's internal bore is suitable for the probe or capillary diameter, and that the locking mechanism (often a compression ring or gland) is intact. This coupler does not contain any electronic components; it is a purely mechanical part. Its role is to hold the temperature sensing element firmly in place, ensuring accurate readings and preventing leaks at the system penetration. Inspect the sealing surface and threads for damage before installation.