The SCAD file can be used for the dimensions of the sim-card cut-out, I used the datasheets for these dimensions. If you want to make any custom tray, they are easy to adapt to your needs.3FF is the 3rd form factor, this is used in more modern phones. 4FF is even smaller and its use will become more prominent over time. Both of them are in the SCAD file as modules that you can use.