922-9878 27 inch Mid 2011 iMac - A1312, Mechanism NB-2884W
This is a replacement hinge mechanism for the 27-inch iMac released in mid 2011. If you are having an issue with adjusting the angle of the monitor, you may need this replaced.
Apple part number: 922-9878
922-9878 27 inch Mid 2011 iMac - A1312, Mechanism