That is just an example.. they come in sizes for removing bolts from M4 (smallest) to M30 (this is some serious stuff!). They have tapered left hand thread that as you turn them into the loosening way it will bite into material of the bolt, wedge itself in, lock into place and for sure it will at some point turn the bolt loosening it. The size of this thing is accordingly to the size of the thread not of the head.
Works every time, I have used it numerous times especially in broken bolts to remove the rest of the bolt still inside. Well that's why it's called a SCREW/BOLT EXTRACTOR
I've used the larger sizes to remove freewheels whose bodies have been damaged so the standard pronged remover no longer engages. You remove the axle, jam the extractor into the freewheel body, clamp in a bench vise and go at it.