The International Electrotechnical Commission has published the IEC 60297-3-108 standard. IEC 60297-3-108 ed 1.0 applies to “Mechanical structures for electronic equipment – Dimensions of mechanical structures of the 482,6 mm (19 in) series – Part 3-108: Dimensions of R-type subracks and plug-in units.” The standard is available for purchase on the IEC website.
“IEC 60297-3-108:2014 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). Key words: R-Type, Subracks, Plug-in unit.”
*Description from IEC Website