The Draw-Tite Class III receiver, part # 75087 does indeed include all necessary installation hardware.
If you were planning on towing with your ML320, you'll also need the following items:
Trailer wiring harness with 4-pole trailer connector, part # C59496
Ball mount, part # C45010
1-7/8 inch trailer ball, part # 19260
2 inch trailer ball, part # 63845
Pin and clip # PC3 or locking hitch pin, # e98882
I've linked you to an install video showing the hitch being installed on a ML320... view full answer...
If the brackets that come with the Draw-Tite Max-Frame Trailer Hitch Receiver # 75087 were listed under the hardware then we could sell you a hardware kit with part # RHK, but since these are considered part of the hitch itself those brackets won't be included in a hardware kit so you'll unfortunately need to purchase the whole hitch receiver kit to get those brackets. view full answer...