Abstract: A fluid flow control device and a compression member therefore permit the clamping of a seal of the device without the presence of internal threads so that high purity can be maintained. The compression member comprises a first suface centrally located on one side of the member for applying a concentrated central force to the seal and a diametrically larger second surface on a second side of the compression member opposite the first side. At least a radially outer portion of the second surface is elevated with respect to a radially inner portion thereof to provide a contact surface upon which the diametrically larger force is applied.