A document that explains the multiple functions of the range spacer, also provides some examples:
https://www.frenchranges.com/wp-content/uploads/2014/10/Lacanche-Range-Spacer.pdf

How to install the Island style spacer:
https://www.frenchranges.com/wp-content/uploads/2014/05/Island-Spacer-Installation.pdf

How to install the Wall spacer:
https://www.frenchranges.com/wp-content/uploads/2013/10/BackSpacerInstallation.pdf