Wheaton Safe-Grind Tissue Grinder, model Z190179 is manufactured by Wheaton Industries. This product is Potter-Elvehjem type. The transparent plastic coating protects the mortar from scratching or inspection, provides firm grip and improves safety in the event of cracking. The PTFE pestle is mounted on a 1/4 in diameter. It can be autoclaved completely. The grinding chamber clearance is 0.004 to 0.006 inches (0.1 to 0.15 mm).