In general, you are prohibited from traveling with sharp objects in your carry-on bags. Multi-tools (multipurpose tools) with knives of any length are prohibited. Please pack these items in your checked bags. Multi-tools (multipurpose tools) with scissors less than 4 inches may be placed in carry-on bags.
but don't forget (☞゚ヮ゚)☞
The final decision rests with the TSA officer on whether an item is allowed through the checkpoint.
I've also always thought that was a cost/theft issue, but I wonder if its also to prevent people from trying to use the hook-type hangers from hanging things from fire suppression sprinkler heads.
Good point. I recently stayed somewhere with a bolted sign by the sprinkler heads that said not to hang anything on them, lol. Makes me think it happens...a lot.