Haloing is a contamination defect that appears on fiber optic end face connections. If present, using a fiberscope to inspect an end face will reveal a discolored ring usually midway between the fiber core and the leading edge of the chamfer. Knowing what each zone means and why the rules tighten as you approach the core is the difference between passing inspection and shipping a connector that will fail in. It's crucial to inspect, clean, and reinspect fiber end faces before mating connectors — whether on patch cords and trunks within the network or on the test reference cord you connect to your tester. Contaminated fiber end faces can cause signal loss and reflections that degrade network. To evaluate the quality of optical fiber connectors, it is necessary to measure the shape parameters of the connector pin body end face after grinding and polishing, including three important parameters: radius of curvature, vertex offset and core depression. Each zone has distinct criteria for acceptable defects, which we will discuss in detail. There is some debate about the necessity of removing the.