The PCWI BRUSHINTERNAL305 Internal Circular Brush Electrodes for Porosity Holiday Detectors, 12" / 305mm Diameter, 340mm Brush CPBE-0159 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.