Abstract: A twin blade mounting and tensioning apparatus is disclosed wherein twin inside diameter cutting blades for sawing crystalline rod materials are mounted with annular clamping-tensioning members which clamp the twin blades between the members with the clamped twin blades having an outer annular shim and an inner annular shim located therebetween in a spaced apart relationship defining an annular fluid expansion chamber, the annular clamping-tensioning members having recessed annular chambers in circumferential alignment with and located axially outward from said expansion chamber, the expansion chamber separated from the recessed chambers by the twin blade walls which are flexible and deformable within said recessed chambers through the action of pressurized fluid means.