first, and mostly, you need times of "me time".

When hes like this, are there any simliar triggers that have a pattern?
It is certainly rough, my parents had such a horrible time with me. and it seemed to get worse in adolences. the chemicals in the brain during puberty can really mess things up. and those who are a male, they tend to lash out more in aggressive, while females tend to verbally lash out, but take the physical onto themselves. (however, that isn't a set thing, just a common theme. as either can be either way).
Is he currently on any meds? any certain consistent food or drinks?
and it doesn't sound mean at all, that you wont allow yourself to be manipulated by him. Its actually a very good thing. even if he may see it as being "mean", it's not. later on in adulthood he will likely notice this as well. And by not allowing yourself to be manipulated by him, actions and behaviors wont esculate as they would if he was "encouraged" to do so, by being awarded (getting his way) in these moments.

Something when in school i've seen (i was often in classes that had others on the autism spectrum, along with down syndrome), the teachers would have a part of the room sectioned off. had a box like shape with walls around it, with an opening just big enough for a person to stand in the opening area. there were no doors. but also none of these kids were more taller or more stronger than the teachers at this time. and normally they would have more than one teacher handleing it. and the wall had about a foot opening from the ceiling all the way around. this area was empty, and allowed a person to retreat to when they were in need of getting their actions under control. i dont know if something like that could be possible in this situation, but i thought of mentioning it.

the threatening of cutting himself tho.. it means one of two things (or both), one being he's thinking on it everytime, which might lead to actual actions if its not addressed (however, letting him have his way isn't going to "address" this and make it any better either. so you are certainly doing the right thing by not letting him control you in this way), or he doesn't realize what the words hes saying really means, he might be saying it just from watching or seeing others do it in times of distress and how they might of gotten their way with it.

Have you ever after trying to speak calmly with him, and he gets worse, after hearing him until he pauses, have you tried to just leave the area without any further words to him? if he follows and continues the fight then that would likely mean what is being dealt with is more than just what can come from being an aspie in distress.

is there any bully-ing or any passive attacks being made on him while he's at school?

If it comes down to it, calling the police may be neccesary to insure both your safety and his. and if they are called in, you will want to tell them about his diagnoses on the autism spectrum so they know what they are coming in dealing with (as "normal" ways they come in to deal with things, are quite different when it comes to an unstable person on the spectrum).

but by not letting him manipulate you, you're doing the very best thing (for both you and him)!