The PCWI BRUSHINTERNAL102 Internal Circular Brush Electrodes for Porosity Holiday Detectors, 4" / 102mm Diameter, 127mm Brush CPBE-0154 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.