double butted

A tube without a butt has constant wall thickness; it is called a straight gauge tube. A single butted tube is thicker at one end; double butted tubes are thicker at both ends (each end of the same thickness) 

What grade of steel is used for the frame?  Is it double-butted?  Thanks,

Butted frame tubes are internally thicker at the ends where stresses are higher and thinner in the center. Butting makes tubes both strong and light. Double butted tubes are butted at both ends.  

Cargo bike.

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