This book is about the design and analysis. While lots of books out there teach short cuts of application without bothering if the readers will have a true knowledge about the subject or not, I choose different path. This book is written with the intention that if the readers follow the discussions, they will understand the fundamental concept of stress analysis, while working with coil and leaf spring is just one of the application of the concept. This approach is used because FEA is essentially a numerical tool for solving differential equations that describe many engineering problems. However, there is a DANGER in using this without proper understanding of the theory behind them. In the past, FEA was taught only to graduate students who would carry out research in that field. Students focus on theoretical aspects of theoretical development and numerical implementation. Nowadays, many universities teach FEA to students at junior level/senior level. Therefore, FEA became notoriously implemented incorrectly.