What is the maximum size fillet weld for lap joints less than 1/4" according to AWS D1.1?

The maximum size for a fillet weld in lap joints where the thickness of the members being joined is less than 1/4 inch is indeed 1/8 inch, as specified in AWS D1.1. The reasoning behind this limitation lies in the strength and performance of the weld in relation to the base materials. For members with thinner sections, a smaller weld size ensures adequate penetration and bonding without introducing excessive heat, which could adversely affect the material properties or lead to distortion. A fillet weld larger than 1/8 inch on such thin materials might not be effectively supported, potentially compromising the integrity of the joint. This regulation helps maintain the structural reliability of welded connections in thin-gauge materials.