What markings are typically present on fuel gas regulators?

Fuel gas regulators are marked with specific color codes to provide essential information regarding their usage and compatibility with various types of gases. The correct answer identifies that gas regulators typically have red markings and left-hand threads.

Red markings serve as a visual cue indicating that the regulator is intended for use with fuel gases, which include acetylene and other flammable gases. The left-hand threads are a safety feature specific to fuel gas applications, preventing accidental connection to incorrect gas supplies. This is critical because the misuse of gas regulators can lead to hazardous situations, including fires or explosions.

In contrast, the other options presented do not align with the established standards for gas regulators. For instance, purple markings are not recognized in standard gas color-coding; green is often associated with oxygen services, and blue markings do not correspond to common gas identification practices. Understanding these markings is crucial for ensuring safe operations in environments using oxyfuel cutting and welding processes.