Thread forms and surface finishes in electrical fittings

Run-on, identifying himself as a Virginia master electrician, describes problems with substitute fittings supplied for rooftop units. A nipple is a short pipe connecting fittings or boxes. His examples distinguish tapered threads from straight-cut threads and smooth internal surfaces from seams or sharp edges that could damage conductors. He also compares galvanized electrical fittings with the untreated material used in the substitute parts. In his account, extending the threads on replacement fittings without tapered threading dies spoiled the replacements as well. The practical issue is whether a readily available substitute retains the features needed for its intended application.