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