How can acetylene fittings be identified by their thread type?

Acetylene fittings are specifically designed with left-handed threads. This unique feature is vital for safety reasons, as it helps prevent the accidental connection of acetylene hoses with hoses for other gases that may have right-handed threads. The left-handed thread configuration is a crucial safety measure because acetylene is a highly flammable gas and ensuring that only the correct fittings connect to its supply line minimizes the risk of dangerous leaks and potential combustion. Using standard right-handed threads for acetylene would increase the chances of mistakenly connecting incompatible gas types, which could lead to hazardous situations. Thus, the identification of acetylene fittings by their distinct left-handed threads serves both a functional and safety purpose in HVAC applications involving gas handling.