Die Kit Blank /6 930 for North Star extruder All dies are made of 1/2'' thick UHMW (Ultra-High molecular weight polyethylene, which is extremely wear-resistant and completely non-contaminating. The top edge of the die cavity is beveled to compact the clay as it passes through, giving a crisp, more solid extrusion. In the hollow dies, there is a bevel on both the interior and exterior portions under each side of the bracket (which holds the center of hollow dies) that helps the extrusion to "heal" after it has been cut apart by the bracket. this bracket fits into a Z-shaped slot machined into the top of the hollow die and is held in place by the barrel of the extruder. If a hollow die is mounted in place, the center part of the die is in exactly the right place and the wall thickness will automatically be even all the way around.