AMRE5006 6" long extension tube with internal cable management (50mm diameter). This extension tube will allow you to lower your projector installation height by 6". These tubes can be combined with any of the same series (6",12",24") to allow different lengths. eg. Combine a 6" and 12" to extend your total extension distance to 18" or perhaps you need 4ft by combining two 24" tubes.
Please note that the projector mount (AMRP100, or AMRDCP100KIT) has about 8.5 inches of drop so the extension will add to the total length. The tube can help lower the projector to your desired height from the ceiling if you do not want to rely on screen height or lens shift/keystone adjustments provided by your projector.