The ornamental design for a slidingunderbarextrusion for roof rack, as shown and described.
FIG. 1 is a perspective view from above of a sliding underbar extrusion roof rack showing the design of the invention. In this and other drawing figures, the broken away portions represent that no particular length is claimed.
FIG. 2 is a perspective view from below thereof.
FIG. 3 is a front view thereof, the rear view being a mirror image.
FIG. 4 is a side view thereof, the opposite side being a mirror image.