Hi,
I guess that one of the best command to put a line of any size is the \rule.
You can control the length the position and the thickness of the line.
Put the code below in a latex file and test it to see what happens. Then change the numbers and ...
Text\rule[-0.1cm]{5cm}{0.01cm} Text\rule[-0.1cm]{3cm}{0.01cm}
Regards
Ariovaldo