A design guide for bolt engagement in cast iron has been developed. The design engagements are sufficient to insure that if a bolt is overloaded and failure occurs, either at assembly or in service, the bolt will break rather than strip the bolt or cast iron threads. In addition to the design guide, this report presents information concerning: 1. The ratio of gray cast iron shear strength to tensile strength. 2. The ratio of shear strength to tensile strength for SAE Grade 5 and Grade 8 bolts.