IEC 60372:2020 is applicable to locking devices used with ball and socket couplings of string insulator units and used with the corresponding metal fittings standardized in IEC 60120, when they are supplied separately.The object of this document is - to define the shapes and some standard dimensions for locking devices, - to define the test methods for locking devices, - to state the acceptance conditions for supply, - to give other dimensions for guidance of manufacturing only. This fourth edition cancels and replaces the third edition published in 1984. This edition includes the following significant technical changes with respect to the previous edition: a. Two new designated size of couplings, 36 and 40, were introduced; b. the relevant content of the 28B W-clip was deleted; c. Annex A is informative, Annex B is normative, Annex C is informative.