This is an essential componet for Cisco Certification labs with 2500 series routers.  These are to convert your Ethernet AUI ports to the RJ-45 style Ethernet ports on your Cisco 2500 Series Routers. You do not need these if you have a Cisco 2505, 2507 or 2516 Router as they have a built-in Ethernet hub. Without these, you cannot plug an Ethernet patch cable into your router in your Cisco lab!!