Abstract: The device comprises a metal fastener which bears against the flange of the rail and against the rail support. An insulating element is combined with the fastener for insulating the fastener from the support and insulating the fastener from a fixing bolt which extends through an aperture in the fastener and is anchored in the rail support. The insulating element is in one piece and comprises a planar branch having an aperture for the passage of the fixing means and a loop portion which is so shaped as to ensure the elastic mounting of the insulating element on the fastener and to be interposed between the fastener and the support.