>>Update. Found this https://github.com/FortAwesome/Font-Awesome/wiki/Upgrading-from-3.2.1-to-4 - will try to follow.
>>
>>Hi everybody,
>>
>>Does someone have a link that shows the old names for the icons and new names for the font-awesome icons? Apparently, they renamed all the icons and I'm going to fix all our references in the application but this cheat sheet would be extremely helpful.
>>
>>Thanks a lot in advance.
>
>I'm trying to find out what "icon-1x" should be changed to. Does anyone know?
>
>Thanks.

The link says 'icon-2x to icon-4x' replaced with 'fa-2x to fa-4x' so maybe it's 'fa-1x' ?