It has a thick rubber shim in it and the derailer was mounted on my Sam, whatever that ST diameter is. I can measure tonight.
IIRC the cable runs from m the shifter, along the downtube, under the bb up along the ST to the the top of the derailer thru the pointy channels that hold it over the top of the assembly, cable then runs down the other (drive side) side of the assembly to the pinch bolt.