I'm sorry, Bill. I don't have the gun with me to measure the hole distances. When I googled the name I found quite a bit of information on the nydar sight. Try Nydar model 47. The inventor apparently was in the airforce in WW2 and took the reflective sight idea used on the gunners machine guns and transferred it to shotguns. It looked to be fairly popular for a short time. My father said that you have to hold your cheek off the stock to line up with the sight. That may be why it died out. Perhaps if the stock was designed to use one or if they had made a quick detachable mount for it it might have been more successfull.