Hummer 2004 H2 Owner's Manual page 287

Receiver Extension (If Equipped)
Use the receiver extension with the front receiver and
various light-duty accessories such as bike racks.
Notice: Do not attach accessories or cargo that
weigh more than 240 lbs. (108 kg) to the receiver
extension. You could damage the receiver extension
and/or your vehicle's frame components.
The receiver extension was not intended for heavy-duty
use, such as trailer towing, winching or vehicle
recovery.
To use the front receiver with the receiver extension, do
the following:
1. Locate the receiver extension (A) in the rear of the
vehicle where it is attached to the spare tire
mounting plate.
2. Loosen the wing nuts (B) holding the extension to
the spare tire plate and remove it.
3. The extension attaches to the front receiver exactly
as the power winch platform does. See "Power
Winch Platform" following in this section.
4. Attach the accessory you will be using to the
receiver extension.
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