Originally Posted by
lysander
As to the question of why Carpenter 158 was chosen as the material for the bolt, rather that an AISI standard steel alloy (like 9310), here is something I was once told by an engineer at one of the big aerospace component companies. Manufacturers, especially those in the aviation field prefer to use proprietary standards, rather than institutional or Federal standards if they can. Proprietary standards, for something like an alloy composition, are owned by the company and usually trademarked, thus changing the composition is highly unlikely. Further, with a single source, they have some leverage to keep the composition from changing - "I'll only be buying from you as long as you don't change the product."
Institutes, associations and other such organizations, like the American Iron and Steel Institute, do not manufacture anything and, theoretically, can change their specifications on a whim if they see fit. This could mean that the 9310 bought today is not the same as the 9310 bought next year.
Manufacturers fear not have tight control of their material supply. While this is a logical concern, especially in the aerospace industry, it is really not something I have ever heard of; a specification changing so drastically that it is unfit for applications that previously used it, but that seems to be the way some companies think.