> threads, not the whole board. How do I proceed?>
<http://www.dragonsfoot.org/forums/viewforum.php?f=50>

You look at the urls of start page and continuation pages and create a filter.
The conntinuation page 2 was:
<http://www.dragonsfoot.org/forums/viewtopic.php?f=50&t=26882&start=15>
Common is f=50 so filter: -* +*f=50*