Abstract: An X-control gage for measuring the X-dimension of hydraulic tube fittings comprises a pin slidably engaged in a body part. In use, a lowermost end of the pin makes contact with the tube stop of the fitting port while the body part makes contact with the inner taper of the fitting along a circle having a specified "B"-diameter. An upper end of the pin extends beyond an upper end of the body part, and measurement of the distance of extension is simply related to the X-dimension of the fitting using a calibrated overall length of the pin and a calibrated dimension of the body part. Methods of calibrating and using the X-control gage are presented, as well as a method of connecting two hydraulic tubes so that there is no loss of hydraulic liquid or pressure at the connection.