Is the 3 or 4 times the wall thickness measurement the radius of the fillet taken where the two tubes meet? Lets say the tubes below have a .035 wall thickness(probably pretty close since its a tt and ht) then the radius at the fillet is .105. Is the radius/thickness of this fillet too small to be structurally sound with the penetration shown? I'm trying to get an understanding of what a small, structurally sound fillet looks like.

thanks, Brian