Jacket color is a quick way to tell the two apart. You can also check the labeling on the cable jacket — for example, “OS2 9/125” indicates Single Mode, and “OM3 50/125” indicates Multimode. This guide explains how to identify them by appearance, labeling, and technical specifications, helping you make the right choice for your installation. Although they can do the same job in some instances, the different construction methods make each of them better suited to certain tasks and budgets. That makes picking between single mode and multimode fiber optic cables an. Distinguishing between single-mode and multimode fiber optic cables can be done by considering several factors. Here are some methods you can use: Single-mode (SM): Typically has a smaller core diameter, usually around 9 microns.