What do you mean by "lock a posting". A posting is a single statement typed by a single user at a single moment in time. Do you mean lock it from being modified?

So I looked and saw the "lock" icon at the bottom of the first posting of the thread. So if I click on that, it locks the entire thread? I never saw it anywhere else (it wasn't in any other posting beneath that first posting). And by the way I use table view as the default.