IEC 61333:2019 specifies marking locations and a coding system of marking on ferrite cores. An alphanumerical marking printed or attached to cores reduces the risk of incorrect assembly, mixing of materials and/or mixing of gapped cores on an assembly line. The markings of the inductance factor AL value or of the gap length are especially important to avoid this kind of problem, and their coding system is specified in this document. This edition includes the following significant technical changes with respect to the previous edition： a) the title of the document was changed; b) the scope of this document was expanded; c) the marking position instructions for ring cores, planar cores, RM-cores, PQ-cores and pot-cores were added in Clause 4 with a few additional descriptions; d) the four-digit-maximum limit of material identification code has been deleted in 5.2; e) in Table 1, the unit of AL has been changed from "nH" to "nH/N2".