Specifies six types and 25 sizes of glass stopcocks, including burette stopcocks. Gives full dimensions and constructional details for a good quality stopcock but, in accordance with current practice in British Standards for volumetric glassware, these details are included for the guidance of manufacturers instead of being mandatory. Includes a leakage test and limit for an ungreased stopcock which should ensure that it can be rendered free from leakage by the application of a minimum film of lubricant.