Horizontal Rulers can be used to Seperate one line from another by putting a Hard line in between text
So this was Ruler line
One can also fix the Length of Ruler line with WIDTH parameter
So This was 150 point Horizontal Ruler line
Yes! by default it takes CENTER alignment, We can change even this to LEFT or RIGHT or CENTER
following are the examples

So this is left Aligned Horizontal Ruler

this is CENTER Aligned Horizontal Ruler
this is RIGHT Aligned Horizontal Ruler with 50% percentage WIDTH parameter

by specifying SIZE of ruler one can increase Thickness of line

And by putting NOSHADOW it gives shadowless ruler