Interchangeable Mini-Lab head with 45/50 bottom joint, PTFE-Clad. No grease needed, will not freeze. Top 19/38 center joint, and are 14/20 side necks are ground. See 9443-20 for head with PTFE-Clad bottom joint and polished top joints. Side arms are placed at proper angles so that the thermometer or addition tube may be placed in the flask without interfering with the stirring unit. For use with 9448-50 or 9450 Flasks.