KPG stirrer assemblies comprise a KPG stirrer shaft and a KPG bearing sleeve. KPG bearing parts are manufactured with high accuracy and uniformity. The specified tolerances for nominal diameter and fit are maintained by careful checks. This guarantees the interchangeability of the KPG bearing sleeves and KPG stirrer shafts. Due to the low bearing clearance between the running surfaces, almost absolute sealing and completely quiet running can be achieved with suitable lubrication. KPG stirrers are an alternative to magnetic stirrers and are suitable for use with reaction vessels that are not accessible from below when very viscous reaction mixtures are to be stirred or a high stirring speed is required.