I updated my desktop machine to Centos 7.4 and my desktop icons were suddenly huge!
After a bit of plugging around I found the fix
Find the application “dconf Editor” under Applications – System Tools *
Drill down to org – gnome – nautilus – icon-view – default-zoom-level
Turn off the “default value” and set the “Custom value” to what you would like
* If you dont find the “dconf Editor”, you need to use the Applications – System Tools – Software application to install the “dconf-editor” package