Spacing of hline after text depends on letters extending past baseline

Question

In the following code, the hrules are different distances from the baselines. The first hrule is at the baseline of the text and the second is at the bottom of the y. How can I make them the same whether or not letters extend past the baseline?

Section x
\hrule height 0.5pt
\vspace*{1cm}   
Section y
\hrule height 0.5pt

Also, why is this behavior happening? Even if I put a vspace{2pt} between each Section x/y and hrule, the spacing between the text and the lines varies. I thought vspace created a space starting at the baseline of the text.

Edit: One solution I have found to get an hrule at the baseline is to do

Section y
\\ \vspace{-\baselineskip}
\hrule height 0.5pt

but this is kind of hackish.

Answer 1

Seems that the \hrule is vertically stacked with the previous text. The y has a depth, while the x doesn't has one. I would add a \strut behind each of the two texts to force a constant (and maximal) depth for both.

Section x\strut
\hrule height 0.5pt
\vspace*{1cm}   
Section y\strut
\hrule height 0.5pt

Answer 2

An answer to your comment would be to use a macro:

\newcommand{\rulesection}[2][2pt]{% \rulesection[<len>]{<section title>}
  \hrule height 0.5pt% top rule
  \vspace*{#1}% top space
  {#2}% section title
  \vspace*{#1}% bottom space
  \hrule height 0.5pt% bottom rule
}%

Using this, the following minimal example

\documentclass{article}

\newcommand{\rulesection}[2][2pt]{% \rulesection[<len>]{<section title>}
  \hrule height 0.5pt% top rule
  \vspace*{#1}% top space
  {#2}% section title
  \vspace*{#1}% bottom space
  \hrule height 0.5pt% bottom rule
}%

\begin{document}
Section x
\vspace*{1cm}
\rulesection[0pt]{Section z}
\vspace*{1cm}
\rulesection{Section y}
\vspace*{1cm}
\rulesection[5pt]{Section p}
\end{document}​

produces

Modifying \rulesection to use {\strut #2} rather than {#2} would produce a more consistent spacing, as mentioned in Martin's answer.