I don't really know what the yellow piece is. It is definately not a ball bearing. It could be a plastic spacer designed to do the same job but I would recommend the ball bearing because it won't wear the body out as fast. Airsoft parts has one http://www.airsoftparts.ca/store2/in...roducts_id=310
. A little more expensive, but it's definately the one with the bearing and I trust them over Evike.