5x4

I tried to use my second large format camera tonight, and met an unexpected hitch, the tripod mounting screw is for a bigger thread than 3/8-16. It looks to be about 1/2" diameter does anyone know what thread this would be?

I've long been tempted to get one of the sliding adapters (made by Fotodiox & others) to use one of my digital camera on one of my 5x4 monorail, but I've heard of issues: Vignetting from the cameras mirror box An inability to focus to infinity with shorter focal lengths The area covered is...