My understanding was that the fillet size was measured along the tube surface. Joint crotch to thin edge of the fillet. So a joint with different tube wall thicknesses would have a fillet with different lengths (or a fillet that was a "French" curve in shape). But I really think that when people start to delve this deep into the structure and design of joints their process gets to the point that they build strong enough joints. Or that the caring to learn of the science make one try to get the hands on righter then those who don't bother to think much about things. Andy.