.404 chain uses a 7/32" file
Regular 3/8" chain uses 7/32" file but the Stihl book calls for 13/64" file on regular 3/8 pitch RS/RM chains but I just use 7/32" file on them.
.325" uses 3/16" file
3/8" low pro or pico uses 5/32" file
Some 3/8" chains need a 3/16" file, and some .325 ones a 11/64" (4.5 mm) file. I also agree with Stihl about the 13/64" file on RS/RM etc in 3/8".