4 Bolts is when you use clamps and will look similar to this. And without the brake the mounts on the frame will look like this But 2 bolt is also know as the evo system, which is so you can have a magura on a vee brake mount. Overall 4 bolt is better and evo (2 bolt) is only for vee frames/forks. Also the Hs33 is better because the lever is better quality and has the "TPA" turbo pad adjuster system which is pretty vital IMO.