A polymer extrusion crosshead assembly for forming a spirally-striped extrusion. The assembly includes conventional components for admitting, turning, and accelerating primary molten polymer toward a novel rotating die sub-assembly. A body element includes an axial counterbore for receiving a manifold supply block in communication with a source of secondary striping polymer. A wear plate is attached to the manifold block. The die sub-assembly includes a striping die having an annular passage for conveying the primary polymer to form an extruded tube or a core material coating. The die is loaded against the wear plate by a Belleville washer. The die includes one or more striping nozzles in communication with the manifold block for injecting secondary striping polymer into the annular stream of primary polymer flowing through the die, creating a longitudinal stripe of striping polymer. Rotating the die while extruding both polymers yields a helically striped (spiral) extrusion.