The PCWI BRUSHINTERNAL254 Internal Circular Brush Electrodes for Porosity Holiday Detectors, 10" / 254mm Diameter, 289mm Brush CPBE-0158 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.