This is what I found after googling for it:
https://www.fonts.com/support/faq/install-truetype-fonts-windows-7
As others have pointed out, OLFSimpleSans is the default single line font.
If you're trying to engrave using CAM you will have to dissolve the text in order for it to be recognized but then you're stuck if you need to edit the text afterwards because it's just lines and arcs. A better solution is to download and install CAMWorks.ttf (available for download from many places online) which allows full CAM functionality without the need to dissolve.
Hi Vijay Gowda,
It depends on whether you have such a font installed on your windows system or not.
Solidworks uses system fonts and which are stored in
C:\Windows\Fonts
(windows 10)
I didn't find a Single Line Font installed by default on my system.
So to use one you have to download a font file and copy it to C:\Windows\Fonts
Eddy