This intermediate specification includes the characteristics, values, as well as inspection requirements for magnetic oxide cores of established quality formed by at least two parts that constitute a closed magnetic circuit for inductances and tuned transformers for professional and industrial applications. Select from the UNE 20-678/1 and UNE 20-580/1 standards the appropriate test methods to be used in the particular specifications derived from this specification, and in accordance with the corresponding particular framework specification. Cores covered by this specification can be used with a regulating threaded stem for inductance or timing effects.