Wheaton Safe-Grind plastic coated tissue grinders afford an added measure of safety over uncoated glass tissue grinders. The heavy plastisol coating protects the mortar from becoming scratched or checked, and assures you of a sure grip. More importantly, the plastic coating creates a greater safety factor in case the mortar cracks or breaks during power homogenization. The transparent coating allows an unobstructed view of the homogenate during grinding. Wheaton Safe-Grind tissue grinders are fully autoclavable. Grinding chamber clearance is .004 to .006 inch (0.1 to 0.15 mm). Diameter of the stainless steel shaft is 0.25 inch (6.3 mm).