In some niche custom PC circles, "Hard Series" can refer to rigid components like: Rigid (Hard) Tubing : Components for water-cooling loops. Custom Case Tops
Usually measured in microns or millimeters. A true "Hard Series" protector should be at least 0.5mm to 1.0mm thick. a4u hard series picturel top
: If the unit produces false outputs, check for static electricity discharge on the mounting panel or interference from nearby high-current equipment. In some niche custom PC circles, "Hard Series"