Piper has issued a mandatory Service Bulletin for owners of most models of PA-28, -32, -34, and -44 involving the main wing spar hardware.

From Piper Aircraft Service Bulletin No. 1366:

All threaded fastener stack-ups common to the wing spar and spar box are located to provide a positive nominal clearance from the radii of adjacent structure. However, depending on the type and orientation of washers installed, due to normal manufacturing tolerances, the outer edge of the washer that is installed against the structure may ride up into the adjacent radius of the structure.

This service bulletin provides instructions for inspecting the washers in the hardware stack-up that are common to the wing spar and spar box for proper configuration, as well as verifying positive clearance of the washer from the radii of adjacent structure.

The inspection is required at the next regular interval, with a maximum of 100 hours.