more information on bits please

I need as much possible education on bits as I can get... I read the thread about bits and that was great. Can any one point me to an all informing website? Or book? Or tell me what you know about shanks? My horse used to be in a slow twist o ring but I have only a simple snaffle.... I just don't want to be overly harsh on his mouth.

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Or the book, I have this book and is EXTREMELY helpful Amazon.com: The Complete Book of Bits & Bitting...