Abstract: A disc is firmly clamped to the end of a rotatable spindle by a coaxial clamping plate spaced from the spindle end by a ring between the plate and disc surface and attached to the spindle by a single coaxial bolt. The flexible plate, thicker at its center than near its periphery, has a substantially flat inner surface which, when stressed by tightening of the bolt, is deformed without exceeding its yield stress to the point where its center section contacts the spindle end surface to provide a constant predetermined clamping force evenly around the disc.The disc and spindle assembly is rapidly and accurately balanced without loosening the clamped disc from the spindle with an adjustable balancing bar which is attached to the head of the coaxial bolt and which may be properly adjusted by the use of a conventional balancing system which can indicate magnitude and direction of the imbalance.