Possible with robots.txt?

[Aforum]

I own a forum that has thousands of individual posts indexed that I would like to get rid of. The standard structure is

domain.com/forum/category1/thread.html
domain.com/forum/category2/thread.html

but the individual posts in those categories are structured like this:

domain.com/forum/1-post.html
domain.com/forum/2-post.html

Is there a way I can deny just the posts without effecting the other categories?

[Quadrille]

First check if you can reconfigure the forum not to produce those pages - else robots.txt can do the job, but you'll need to be sure the phrasing does not eliminate vital pages (such as category indexes ...)

Depending on the software you use, there may a support forum that will have expert help (some do!).

But minimising duplicate URLs will most certainly help your forum :)