The obsolete rule of thumb for aerospace design is that fatigue sensitive structural members be sized with a 20% reduction in material properties for both Ftu and Fty. This rule of thumb is ineffective when weight savings are important and a comprehensive understanding of joint fracture failure is required. Fatigue and fracture calculation are very complex, highly nuanced and LugCalc will not perform them. Users interested in exploring lug joint fracture mechanics should investigate other specialized tools and methods.