You may ask moderators and administrators to lock your own threads for you. In most cases, they should do it for you.
You may ask moderators and administrators to lock or unlock other peoples' threads. They may or may not do so.
Threads may be locked for a variety of purposes; these may include (but are not limited to) the following:
* Quality control
* Because the administrator thinks the thread is too long or complex and needs to be many topics instead of one.