MyBB Community Forums

Is there any plugin that can set custom permission for the threads ?
 I mean I want to create threads, In which admin and moderators(optional) allow selected members to take part, i.e. they can only post in it if they have been selected (allowed).
Condition is-

A particular member may have access to one thread while he/she may not have access to other thread in same forum

not sure that such plugin exists for MyBB 1.8.x
however you may try using invite only threads plugin coded for an old version of MyBB

see if required => changing compatibility of plugin to try using on MyBB 1.8.x