specification table Fusion 360

[Aslavakun]

How do I automatically enter the length of the metal profile in the specification?

[jeff_strater]

I think we need a bit more information to answer this question.  Can you share a bit more about your question?  Is this a sheet metal question, or more general?  Share some images that help clarify the question, or even better:  share the design itself, but we need to know what you are trying to do.  Thanks.