Manufacturers AR15 / M16 M4 Carbine Rear Sight Ball Bearing, New (For Adjustable Sight Models; 2 Req'd; A2 Style)
Rear Sight Ball Bearing, New (For Adjustable Sight Models; 2 Req'd; A2 Style)

This part is found in the following schematics

Rear Sight Ball Bearing, New (For Adjustable Sight Models; 2 Req'd; A2 Style)

This part is found in the following schematics