What is the height above the baseline to the middle of an open bracket?

Question

So I have a rule pointing at the middle of the following text. I have achieved this with the following code:

\newlength{\Fraiseheight}
\setlength{\Fraiseheight}{1ex}
\addtolength{\Fraiseheight}{-\Flinewidth}

\newlength{\Fbaselength}
\setlength{\Fbaselength}{20pt}

\newlength{\Flinewidth}
\setlength{\Flinewidth}{0.5pt}

\rule[\Fraiseheight]{\Fbaselength}{\Flinewidth}

The height 1ex is the height of an x in current font. This raises my rule higher than the centre of an open bracket that follows. This looks awkward especially for curly brackets. My question is: What height above the baseline do I need to achieve the following effect: "-(x" or "-{x" where the - is supposed to represent my rule and the x is present to show the discrepancy between the height 1ex and that of the - character.

Answer 1

The middle of the brackets is the math axis. Command \vcenter centers its contents at the math axis.

$\vcenter{\hrule width \Fbaselength height \Flinewidth}$

This is syntax of plain TeX that also works in LaTeX. But it can also be expressed in "pure LaTeX":

\parbox[c]{\Fbaselength}{\rule{\FBaselength}{\Flinewidth}}