How do we know that Avraham Avinu wore a knitted kippah?
According to Breishit 14:22-23: "Avram said to the king of Sedom: 'I have lifted up my hand [i.e. sworn] to Hashem the Supreme God, Maker of heaven and earth, that I will not take anything of yours, from a thread to a shoelace, lest you say: I have made Avram rich.' "
The phrase "from a thread to a shoelace" is apparently an expression for "from the very highest thing on the body, to the very lowest thing". Thus proving that Avraham would normally have worn a garment with threads in it on his head, i.e. a srugi.
Credit for this "insight" goes to R' Yoni Grossman.