as an example, with Tkx i do :

  Tkx::font_configure('TkFixedFont',-size=>8);

.... 

  my $lb = $w_bfrm->new_tk__listbox( -height    =>3
                                   , -selectmode=>'extended'
                                   , -font      =>'TkFixedFont'
                                   );
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I using Tk, anyway thanks for your input.

G'day Evel,

"... I also want to know what the default font style name is?"

You can use the cget() method (see Tk::options) to determine the default option value of any widget.

You can find values quickly using a one-liner, e.g.

$ perl -E 'use Tk; say MainWindow->new->Listbox->cget("-background")'
#d9d9d9
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Some option values aren't individual scalars: you may get a reference returned, e.g.

$ perl -E 'use Tk; say MainWindow->new->Listbox->cget("-font")'
Tk::Font=SCALAR(0x7f972e1bbd80)
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You can just dereference as normal. Here's two examples showing the older "${ ... }", and newer "...->$*", syntaxes. See "perlref: Postfix Dereference Syntax" if you're unfamiliar with the second one.

$ perl -E 'use Tk; say ${ MainWindow->new->Listbox->cget("-font") }'
Helvetica -12 bold
$ perl -E 'use Tk; say MainWindow->new->Listbox->cget("-font")->$*'
Helvetica -12 bold
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Here's another example just to show different widgets have different defaults.

$ perl -E 'use Tk; say MainWindow->new->Text->cget("-font")->$*'
Courier -12
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Also be aware that, while Tk has its own defaults, these may be altered externally (e.g. a .Xdefaults file); or from within your application by a module you've loaded (e.g. a custom widget), or by your own code (e.g. one of the "option*()" methods). See Tk::option for details.

— Ken

Thanks again Ken, good tips about the method of getting dereference value. Yes, so now there are more fonts I can used than before, like 'Consolas', 'Courier','Lucida Console'.(https://en.wikipedia.org/wiki/Monospaced_font)