These precision-crafted grinders with large ground glass wall surfaces are exceptionally well-suited for preparing some of the tougher connecting tissue and muscles. Initial rough grinding occurs at the bottom of the vessel, followed by fine grinding that occurs against the vessel walls. To permit vigorous grinding, the pestles of these units are capable of being mechanically, as well as manually driven. For conditions requiring closures we have a model which features polypropylene screw caps. This model comes with two caps, one accommodating the pestle and the other to seal the vessel.