The Acer chromebook 315 actually doesn't have a write protect screw. It is a CR50 chromebook which means that in order to disable write-protect you need to unplug the battery from the chromebook, then plug it into the wall and turn it on. From there you need to put the chromebook into developer mode and get a terminal by pressing Ctrl+Alt+T, log in and run the command flashrom --wp-disable then open up the chromebook again and plug the battery back in. I did this to put linux on my chromebook, google mrchromeboxtech for more information.