A holding sleeve has a sleeve body having multiple clamping slits, and an outlet portion. The clamping slits are defined longitudinally and radially in the outer surface, are arranged at even angular intervals and communicate with the knife hole. Each clamping slit has a first end and a lateral branch. The lateral branch extends laterally from the first end of the clamping slit and communicates with the clamping slit. The outlet portion is formed in the outer end of the sleeve body and communicates with the lateral branches of the clamping slits.

The invention relates to a collet chuck for clamping a dental tool, wherein the collet chuck has at least temporarily a mechanical stress applied to it and is made of steel.

The collet chuck according to the invention is characterized in that the steel, at least in a surface layer, has a nitrogen content of at least 0.1 wt %.

A holding sleeve has a sleeve body having multiple clamping slits, and an outlet portion. The clamping slits are defined longitudinally and radially in the outer surface, are arranged at even angular intervals and communicate with the rotary cutting tool hole. Each clamping slit has a first end and a lateral branch. The lateral branch extends laterally from the first end of the clamping slit and communicates with the clamping slit. The outlet portion is formed in the outer end of the sleeve body and communicates with the lateral branches of the clamping slits.