Adjust width of spacer between Mac OS dock icons
I just tried typing in different things and discovered that &quot;small-spacer-tile&quot; adds a narrow space.
defaults write com.apple.dock persistent-apps -array-add '{&quot;tile-type&quot;=&quot;small-spacer-tile&quot;;}'
killall Dock

Here, a &quot;small-spacer-tile&quot; vs a &quot;spacer-tile&quot;: