What is the function of the Apache's Strap Pack?
Picture above is from Helicopter Performance, Stability, and Control by Ray Prouty, and shows the fully articulated rotor such as installed in the Apache. The Fully Articulated term means that the blades can rotate in three Degrees of Freedom: fwd/aft, up/down, and nose up/down. The rotation axes are single points of failure: when they break the blade is launched, unbalancing the rotor and rendering flying and autorotation impossible.

The problem with the Apache setup is with eight nuts degrading due to corrosion, as from this link:


  The order came after officials learned that bad weather and salt water in coastal regions could lead the eight “strap pack nuts” on each of the rotary blades to reach the end of their life expectancy sooner than projected. 


Fully articulated hubs are the most common design in helicopters, the others being the teetering rotor such as in the Bell 212 and the hingeless rotor in for instance the Westland Lynx.