The PCWI BRUSHEXTERNAL76 External Rolling Pipeline Brushes for Porosity Holiday Detectors, 3" / 76mm ID - 89mm OD - 2 Wheels EPBE-0168 is used for the verification of porosity or holidays on pipelines or circular surfaces. This external Rolling Pipeline Brush is suitable for all High Voltage Porosity detectors, holiday detectors, spark testers and jeepers.