The r22 rotor blades flap and teeter. The hub teeters on the mast and the blades flap on the hub. Hence the three bolts at the top. At low rpm and low collective pitch, the blades flap all the way down due to gravity and the entire weight of the blade is supported by the little curved ear that contacts the droop stop. That's number 18 in figure 9-3 in the link above. The droop stop is bolted to the mast, so this has the effect of locking the hub from teetering. This keeps the blades from hitting the tail boom during startup and shut down.
It's also why there are placards at the blade tips saying not to pull down. You can't teeter the hub by pulling down because pulling down just increases the friction on the droop stops. They tell me if you pull hard enough, you can break off the little curved part of the blade. If you need to teeter the hub, you push up on one blade, releasing that side from the droop stop. The weight of the other blade overcomes the friction against it's droop stop and teeters the hub down until it contacts it's teeter stop (number 23 in the picture).
Hope this helps.