Center and Off Center is in reference to the center line of roof.
The off center measurement is from the center line of the van to the center of the hole.
Patent Pending adapter matches the contour of the OEM roof so the Maxxair Dome mounts to a flat surface. Prevents distorting the roof sheet metal or vent flange and can be used as an aid for locating the fan. They are CNC machined out of UV and fire resistant expanded PVC. The fan mounts to the outside adapter. The adapter ID is 7" and the OD is 10.5"
The off center measurement is taken from the center line of the roof to the center of the 7" hole.
If you have questions about this product you can call Hein at 541-49O-5O98
Van owner and/or installer assumes all risk associated with roof top mounted items and/or components. Van owner and/or installer recognizes and agrees that this product, and each of its component parts, is sold ?as is? and that seller makes no representation or warranty of merchantability that the product is fit for any particular purpose.