"Tks average" in heat exchanger specifications

[nininini]

Hello,
I would like to know what "Tks-Ave" means in heat exchanger specifications.
It is written next to the outside diameter of tubes and has a dimension of length.
I would appreciate your help.

 

[ione]

Thickness

 

[nininini]

Thank you so much!!!

 

[EdStainless]

Average wall, as opposed to minimum wall

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P.E. Metallurgy, consulting work welcomed