The Apple VESA Mount Adapter Kit is compatible with the aluminum and glass 24" iMac, the late 2009, mid 2010, and mid 2011 27" iMacs, the 24" and 27" LED Cinema Displays, and the 27" Apple Thunderbolt Display. It will allow you to attach your monitor to a separately-sold 100 x 100mm VESA compatible mount, offering more desktop space.
Offers alternative mounting solutions for iMac, Cinema display, and Thunderbolt display
Included tool enables you to remove the iMac or display stand and attach the VESA adaptor