Getting the flit size in a Tiled Chip Multicore Processor(TCMP) system with a mesh architecture

Question

Consider a TCMP system with, say, a 4x4 mesh Network on Chip (NoC) where each tile has a superscalar processor. It is given that that the TCMP uses 64-bit words and the inter-router link bandwidth is 128 bits. So, the size of each flit passing through this network would be equal to 64 bits or 128 bits? I know that flits are the basic units of transfer between a pair of routers. Then would their size be equal to the bandwidth or the word size?