F.55 ISO 50 - Splindle Heads/Motorized Spindle F.55 motorized spindle heads ISO 50 taper. Choice of the type of bearing is according to application: - For drilling and milling applications = F.50.RC - adjustable taper roller bearings pair. - For boring and reaming applications = F.50.CO - set of three precision and pre-loaded angular contact bearings. A range of different tool holders, such as ABS, HSK, etc. can be supplied on request.