The cls_savthr_*.2da files are the .2da files that define the advancement of saving throws for a class. These files are used only when referred to by the "SavingThrowTable" column of classes.2da. These .2da's have 60 rows (numbered 0 to 59), even though only 20 rows are relevant (since saving throw advancement stops depending on class after character level 20). These .2da's additionally have a blank row between the headers and row 0.