When threading black iron pipe for a natural gas furnace, how many threads should typically be cut?

When threading black iron pipe for a natural gas furnace, cutting 7-10 threads is typically recommended. This range provides a balance between ensuring a secure connection and facilitating proper sealing at the joint. The threads allow the pipe to be securely connected to fittings, ensuring that gas flows properly without leaks.

Having too few threads can lead to insufficient engagement with the fitting, increasing the risk of gas leaks. Conversely, too many threads can create complications when connecting the pipes and may not improve the seal significantly. Thus, cutting 7-10 threads strikes a practical balance, ensuring the integrity and safety of gas connections in furnace installations.