thats what i would call them or torx bolt,but i would be surprised if they are stainless as you really want high tensile but you can get it in stainless but it is not cheap.
the way to test for stainless is to use a magnet ,if the magnet does not stick very well then proberly stainless.
BBS split rim bolts are usually chrome plated high tensile steel
well whatever they are these are what you need to get em off. ive jus split some OZ turbos for my mk1 golf using em Pertsch & Partner Onlineshop - Tools