I open the thread to be linked in a different window, so the whole URL appears. Then it is only a matter of copying such URL, and typing:
{url} <insert copied URL here> {/url}
or
{url=<insert copied URL here>} <Insert whatever desired message/text here> {/url}
Just use [] instead of {} and you will have a working link.
Hope it helps.
Cheers,
Pepe