I like the name Hank very much, but I think it's too much associated with Henry; other name sites say it's a nickname of Henry, not of John (except for this site). Besides, Henry is Hendrik in Dutch, and a Dutch nickname of Hendrik is Henk, which is quite similar to Hank.
You can guess I'm having doubts about what this site says; that Hank (short for Hankin) could also be a form of John. I mean, how come Hankin is a different form of John? At first sight, both names don't seem to have anything in common.
I'd be delighted if someone can give me the 100% evidence that Hank is a form of John.
Lucille (formerly Lu, but had to change my nickname in order to get a password)