Hi As I am reading through my textbook on the stiffness for two clamped members, As I am reading about the rotschers pressure cone , there is a sentence that say: "in this book we use alpha(half apex angle) = 30 deg except in cases in which the material is insufficient to allow the frusta to exist" under WHAT condition will not the material allow the frusta to exist? I thought frustum is just the side of the member that we are looking at, how does the material affect geometry? English is my second language so it could be that there's some obvious meaning to these words that I'm not understanding, but I just feel like my textbook always pull out variables and technical terms without explaining what they are. I have spent more time googling than reading the book. anyway, I appreciate you guys' help.