Dear Pablo,
Here is my example:
\setuppapersize[A4]
\setupbodyfont[termes, 12.50pt]
\setuplayout[backspace=2.9cm,
             width=fit]
\ininnermargin{\blackrule[color=black, height=0.10ex, width=1cm]\\{3.2.2}} \dontleavehmode \blackrule[color=black, height=0.10ex, width=13.50cm]
\showframe
\starttext
Me\par
\blackrule[color=black, height=0.10ex, width=13.50cm]\dontleavehmode \inoutermargin{\blackrule[color=black, height=0.10ex, width=1cm]\\{3.2.2}} \par
Me
Many thanks for your help.
Uschi Hermann