This part of IEC 60297 provides dimensions and features for R-type subracks and plug-in units, i.e. ruggedized variants of the mechanical structures of the 482,6 mm (19 in) series, with enhanced vibration and shock resistance and/or improved EMC performance, for use in more harsh environment. This leads to a subrack standard which is externally compatible with IEC 60297-3-100 but internally largely incompatible with IEC 60297-3-101. R-type subracks, chassis integrated subracks and plug-in units incorporate dimensions and features which provide for a higher level of ruggedness, compared with IEC 60297-3-101 (test set-up and load definitions are selected from IEC 61587-1 and IEC 61587-5).