You CAN'T use a nut on the inside.The con rod will hit it. We used crankcase pressure for control line combat and rat race for years. You drill and tap a 4-40 hole in the backplate and screw in that size pressure fitting and then file it flush on the inside. Fox used a pressure fitting on the upper backplate screw. The one that is behind the bypass. That hole went straight into the bypass. The pressure fitting replaces the backplate screw.