Standard Carb Adapter Bore Size?

I know this has to have been covered before, what is the standard size opening on a carb adapter plate?

I talked to the guys at holley, they said 4-1/4" x 4-1/4". When I drew it up in CAD and cut it out it seems like an awfully large opening for a stock holley or edelbrock carb.

Does anyone here have one they can throw a tape on for me???

 

Anyone got one laying around???

 

I just measured a 1" Mr Gasket spacer and got 3-1/2" front to back and 3-5/8" side to side.

Ron.

 

Use a gasket from the carb you plan on running and duplicate the size and contour.

 

Thanks Ron.