Abstract: An improved track and spline or clip member defining a mechanical fastening system for attaching sheet or cover material to the track in a positive manner, wherein the track includes a channel having an improved configuration comprising a base member with a central V-shaped bottom wall surface fluted at the outer edges thereof, inclined inner side wall surfaces, a dual durometer plastic insert clip or spline having a central semi-rigid body member, and integrally formed outer rigid wing members arranged to be inserted in the channel for locking engagement therein with the sheet material being interposed between the track cahnnel and the spline.