This part of IEC 61755 defines certain dimensional limits of a 2,5 mm and a 1,25 mm diameter cylindrical zirconia (ZrO2) PC ferrule optical interface to meet specific requirements for fibre-to-fibre interconnection. Ferrules made from the material specified in this document are suitable for use in categories C, U, E, and O as defined in IEC 61753-1. The contents of the corrigendum of January 2009 have been included in this copy.