כ \ ך Kaf - the 11th letter - gematria value 20
כ is the first letter, out of a set of 5 that has 2 forms. The regular form כ, when not at the end of the word, and the form ך when at the end of the word.
כ is also one of the BegadKephat letters that has a secondary pronunciation. כ is pronounced as K in both Modern Hebrew and Aramaic. The secondary pronunciation in both Hebrew and Aramaic is like that of ח (Khet) in Modern Hebrew. See https://unifyd.tv/community/posts/khet-numeric-value-8-is-the-firs