Out of curious, using a 32GB USB for only one OS installer is really wasteful, so here's a guide for you guys to make full use of it :) Example in this guide: A 32GB USB 4 OS X/macOS installers (Mountain Lion, Yosemite, El Capitan and Mojave) Host machine is Mojave (Laptop Haswell i3 U chip) How to get those installer? For ML, Yosemite, El Capitan you download them from this link with Safari For Mojave (and Catalina), use dosdude1 patcher to download the full .app file. The installer from App Store in my case only download a 14MB file. Preparation Check your SMBIOS FIRST!!! For compatibility, or your machine will get error with the installer. In my case is an i3 4005U Haswell, there are 3 models: MacBookPro11,1 MacBookAir6,2 and MacBookAir6,1 If I choose MacBookPro11,1 I cannot extract Mountain Lion because it is not supported for that model (only Mavericks and above). So I have to change to either MacBookAir6,2 or 6,1 Open Disk Utility -> Erase your USB...