This is the Renishaw M8 Clamping Kit Base Plate #R-KC-C1C-8.
The plate size is: 13mm x 300mm x 300mm. It is used with component C.
The M8 CMM Clamping kits can be used to hold aluminum, plastic, and other nonferrous parts. A kit includes a base plate with M8 threaded holes 15 mm on center (choose from plate sizes) and a set of components (A, B, or C) along with plate clamps for mounting to the CMM.