INTRODUCTIONSelection of the correct fillet weld size is essential for the satisfactory performance of many weldments in service today. Fillet welds are used in virtually every industry@ and when properly designed@ provide effective and efficient connections.Traditional designs base the size of the welds on the allowable unit loads that the welds are expected to experience in the intended applications. For sections of different thicknesses@ the minimum fillet size is governed by the thicker member (references 1 and 2).While this approach is conservative@ the weld sizes may not be the optimum. Fillet welds can be too large or too small and it is important to have the correct size for each connection. As the volume of weld metal is severely impacted by the size of the weld@ each increase in the specified fillet weld leg length has a dramatic effect on the amount of welding required.The larger than necessary welds will increase the amount of welding material@ reduce the speed of welding@ and increase the resultant distortion effects. All of these will have a negative impact on the economy of the work and the overall productivity of the operation.Similarly@ too small fillet welds will not provide the necessary performance for the weldment and will most likely result in repair work being required.An alternative system for calculating fillet weld sizes was presented by two researchers through reference 3. This approach is the basis for this handbook@ and seeks to provide a method for determining the optimum fillet weld size. This document is not a standard.