An improved fastener assembly is provided for mounting railroad trackage on a concrete bed or the like. The fastener assembly of the invention is constructed to include a base assembly which is anchored to the concrete bed. The base assembly is formed of top and bottom plates with an interposed resilient sheet member. The resilient sheet member serves to isolate vibrations between the rail and the track bed, and it also provides for electrical insulation, which is essential in the case of electrically operated railroads. Rail supporting clips are attached to the base for providing a positive attachment between the rails and the base. The assembly is adjustable, as will be described, so that the rail may be set precisely to the desired gauge.