The PCWI BRUSHINTERNAL127 Internal Circular Brush Electrodes for Porosity Holiday Detectors, 5" / 127mm Diameter, 160mm Brush CPBE-0155 is ideal for verification of porosity or holidays in the interior of pipelines or circular surfaces. This Circular Internal Brush Electrode is suitable for all High Voltage Porosity detectors, holiday detectors, spark testers and jeepers.