While we were discussing UX at work, we stumbled across this question. Which icon is the best icon for settings, wrench or gear? We simply just need to figure out which icon is the best for settings and if there’s a difference in that opinion depending on where people live.
Most of the time they can be used interchangeably, and whenever possible add text of some sort to make it more clear.
The wrench does carry some subtle cues, however. For example configuring an application or accessing admin tools. Whereas the cog is more for settings of preference only.
Popular usage: I feel the wrench used to be used more often, but has fallen out of favor for the cog for whatever reason. I know on most applications and webpages now, if I were looking for settings or preferences my first instinct would be the cog or a hamburger icon.
Even though most users would see and understand either icon fine, I would choose the cog / gear for a preferences/ settings icon (along with text). It is slightly less vague and more recognizable in my experience.