Are you trying to set the thread title to be in bold font?
It doesn't work that way. Boldness is set automatically by the system.
When you open a board forum, any topics you have not looked at will be in bold font. Topics which you have already looked at but which do not have any new posts in them since the last time you looked, will not be bold.
If you come back later, and a new post was made to one of the threads, then that topic will again appear in bold font for you.
Whether a topic is in bold or not depends on each user's computer and what they have and have not looked at already.