There's a few things going on with that screw AFAIK. Before you go down the GalliumOS route you can choose between dual booting with a menu or booting straight

There's a few things going on with that screw AFAIK. Before you go down the GalliumOS route you can choose between dual booting with a menu or booting straight into it. I went with the dual boot approach because I still wanted the ability to boot into ChromeOS in case something crazy happened with GalliumOS. In most cases this translates to turning on the Chromebook and hitting CTRL+L which boots you into GalliumOS, as opposed to hitting CTRL+D to boot into ChromeOS. It's a 2 second process to pick the OS to boot from and that's all you have to do. But going back to the screw, it controls at least these 2 things: 1. sudo crossystem dev_boot_legacy=1 is a command that lets you boot something other than ChromeOS. This setting needs to be persisted somewhere. The screw lets it get written to your BIOS so it never gets lost. If you don't modify the screw it gets lost when your battery is 100% tapped out, but if that's the case all you have to do is drop into a terminal when you turn your Chromebook on and run the command again and you're good to go, nothing gets wiped. This only happens if the battery is fully fully drained. 2. If you decided not to dual boot you need to modify the screw to directly boot into GalliumOS.