Most of the letters described below are only introduced in the book Hunminjeongeum and never used afterwards. Also note the IPA sounds are reconstructed and may differ from the actual pronunciation it had, if they were even pronounced at all.
The letters ᄼ, ᄽ, ᅎ, ᅏ, ᅔ, (齒頭音) and ᄾ, ᄿ, ᅐ, ᅑ, ᅕ (正齒音) were designed to be used for transcribing the distinction between alveolar sibilants( /s/, /z/, /ts/, /dz/, /tsʰ/ ) and alveolo-palatal sibilants ( /ɕ/, /ʑ/, /tɕ/, /dʑ/, /tɕʰ/ ) in Late Middle Chinese.
There were 4 variants of consonant letters with ㅇ underneath them, called 脣輕音 (literally "light lip sound"). Those were ㅸ /f/, ㆄ /fʰ/, ㅹ /v/, and ㅱ /ɱ/ or /w/. Only ㅸ was used for writing Korean, and ㆄ, ㅹ, and ㅱ were used for the corresponding Chinese phonemes.
Also lots of compound vowel letters such as ힽ, ㆋ, etc were used to transcribe the triphthong sounds belonging to Chinese or Manchu.