Engineer to Win –
While, once again, more involved than necessary for the majority of people, there are two chapters in this book that should be read by anybody who plans to – or currently does – fabricate their own suspension parts. Carroll does a really great job explaining stress risers and proper bolt use in a way that makes sense for even a casual builder.
Fair warning: you will have to take into consideration that the information in these books is geared toward race cars, but the theories are still relevant.