The TW-12A martin house WDC modified Excluder adapter plate is designed to fit onto most houses to convert them to SREH. The present holes must be enlarged, and then, the adapter plate is attached by 2 screws. The plate measures 3 1/4" tall by 4 1/2" wide. The bottom of the WDC Modified Excluder is 1/4" from the bottom of the plate. The TW-12A sells for $2.50 each plus S&H.