ISO/TR 21704:2017 contains investigations and investigation results on toughness of round steel link chains, tested with sub-size specimens. It applies to round steel link chains for hand operated chain hoists of grade TH and VH and for sling chains used for chain slings of grade 8. NOTE 1 Associated International Standards are ISO 16877, ISO 16872 and ISO 3076. In future it is intended to implement the results on toughness derived in this document in new standards. Eleven steels, provided by four manufacturers, were tested to find a test regime on sub-size specimens and requirements on the notch impact toughness values at design temperature which resulted out of the tests. These requirements are adjusted to the toughness values of full size ISO-V specimens. NOTE 2 The requirements are also valid for other cross sections of the chain than round.