The subject of this book referred to as the bending strength of CATT (circular-arc-tooth-trace) cylindrical gear, is taken to mean the study of the tooth bending stress with the analytical models and testing data. The objectives of this book are to contribute theoretical formulas and experimental methods towards efficient design and analysis of CATT gear in academic research and engineering application. The bending strength formula of CATT gear is developed base on classic mechanics and heritage of the main part of spur gear formula with additional modified factors. It allows calculating the stress distributions along the tooth length at the root fillets for the predictions of the maximum stress and determination of the critical transverse section on the tooth. The strain gauge method is applied to measure the stress distributions along the tooth length at root fillets. It provides a means for the bending stress measurement of CATT gear. The book indicates how to validate the theoretical model by comparing the calculation analysis results with the test analysis results. This book is technically thorough, complete and consistent based on the existing knowledge, measuring technology and validated experience within academia and industry. It provides the appropriate methodology from bending stress modelling to experimental examination for the research and development of new type gear.