Cisco 2960-X 

C2960X-STACK is a Cisco Catalyst 2960-X and 2960-XR Series Switches FlexStack Plus Stacking Module, which allows these switches stack with each other to offer flexible management

FlexStack-Plus is the name of the stacking technology used by the Cisco Catalyst 2960-X and 2960-XR Series switches. FlexStack-Plus is specific to the 2960-X and 2960-XR Series of switches.

Mixed Stacks: FlexStack and FlexStack-Plus

The 2960-S and 2960-X support a mixed stack of 2960 models. All these 2960 models run the FlexStack protocol, allowing them to be stacked together into a single stack. The exception is the 2960-XR does not stack with either the 2960-X or the 2960-S. The 2960-XR has the IP-Lite feature set, and this is not compatible with the LAN Base feature set on the 2960-X and 2960-XR.