Does the curve actually change how the thread pulls, or just the angle?

Did you figure out the number before you walked in, or did you just pull it out of thin air when she asked? That part feels like the whole trick.

My grandpa's 1972 Ford truck still runs fine and nobody acts like that's a miracle. Same deal with tools, the old stuff was built heavy because it had to be, and people kept fixing it instead of tossing it. The 40% number isn't nostalgia, it's just what happens when something works.