All-glass construction in a popular style which affords the choice of hand or motor operation. Pestle is tooled for an appropriately sized single hole rubber stopper (not supplied). By inserting a short metal rod in the stopper, these grinders can be motor driven at slow speeds by inserting the metal rod into the motor chuck. Replacement components are available and completely interchangeable. Clearance between pestles and tubes is 0.004" to 0.006". Manufactured from 33 expansion, low extractable borosilicate glass conforming to USP Type I and ASTM E438, Type I, Class A requirements.