Three classifications are divided equally from the thirty-three letters of the old alphabet:
Common runes: El-Amn (available from normal Hellforge);
Uncommon runes: Sol-Um (available from nightmare Hellforge);
Rare runes: Mal-Zod (only Hel-Gul available from hell Hellforge).
Because there are eleven in each group, they must be divided 3/4/4 in sub-classifications:
Low commons: El, Eld, Tir;
Mid commons: Nef, Eth, Ith, Tal;
High commons: Ral, Ort, Thul, Amn.
Low uncommons: Sol, Shael, Dol;
Mid uncommons: Hel, Io, Lum, Ko;
High uncommons: Fal, Lem, Pul, Um.
Low rares: Mal, Ist, Gul (hell forgeable);
Mid rares: Vex, Ohm, Lo, Sur;
High rares: Ber, Jah, Cham, Zod.
Since Mal and higher are rare, people may refer to them all as HRs, while others only speak of unforgeable runes, meaning only mid-high rare runes are considered HRs.