This kit works with all GV90+ boilers. The 383-500-350 kit is also compatible.
The openings have an ID of 3.5".
The 3" Sidewall Vent Termination Kit for Ultra Gas-Fired Boilers has an inside diameter that is same as Schedule 3 PVC.
The outer edges of the plate measure 1 1/4". It protrudes about an inch from the wall.
Please refer to the following Installation Guide: http://s3.pexsupply.com/manuals/1302724632876/53452_PROD_FILE.pdf