riddle - Large and in charge

Opened or closed, I continue to be.
A mechanism of choice, But I can be beastly.

I come in all shapes and sizes, Each with a common task.
I cling to life by a thread, What am I, I ask?

Added hint:

I can be made out of anything from A to Z, and sometimes have eyes with which I can't see.

Another Hint:

I hate to give another hint but there have been a ton of views and guesses, but here it is:
I have a few close friends, just like a pea, and I jump through hoops for everyone around me.

This is part 1 in a series by the way. The final part will use clues from each.

Answer

You might be:

a button

Opened or closed, I continue to be.

If you are buttoned up or not, you are still button.

A mechanism of choice, But I can be beastly.

Buttons are very often used, but some of them can be very tricky to unbutton.

I come in all shapes and sizes, Each with a common task.

Buttons come in all shapes and sizes, but they are all used to connect two pieces of clothing.

I cling to life by a thread, What am I, I ask?

Buttons are sown to clothes by a thread.

Hint 1:

I can be made out of anything from A to Z, and sometimes have eyes with which I can't see. Buttons can be made from many materials and they can have the holes for thread to be sown.

Hint 2:

I have a few close friends, just like a pea, and I jump through hoops for everyone around me. Buttons usually come in rows, like on a shirt. When you button up the shirt, you pass each button through an opening/hoop.