My Bradco 511 came with the thumb fitting welded to the dipper stick. I think you will always have cracks near a welded fitting on a dipperstick, unless the fitting and dipperstick both are reheat treated to the same hardness. Different hardnesses just invite cracks. I bought my thumb from Bradco thru Mahindra. I can weld (Farm Shop in High School FFA), but just had shoulder surgery and didn't have access to a welder. I do want to buy a good machine to start welding my own projects. Also, the engineering was already done on the Bradco thumb. As you can see in the 1st photo, the Bradco thumb's teeth have an over bite, for those guys that asked how long to make the teeth. The second photo shows the thumb stowed. I have a 12 inch bucket that I never use, as the thumb's teeth don't mesh with it, only my 24 inch bucket meshes with the thumb. The 3rd photo shows how useful the thumb is even when stowed.
hugs, Brandi