In tightening critical structural members such as pressure vessels of nuclear reactors and chemical plants and important parts of diesel engines, a hydraulic tensioner is widely used because of its high accuracy in controlling clamping force. The ratio of the desired clamping force to initial tension, which is termed the effective tensile coefficient, is the most important factor to be predicted in the actual operation of given joint configurations. It is reported, however, that a certain amount of scatter in clamping force cannot be avoided. In this paper, an elementary approach to analyze the tightening process is proposed using spring elements, where the effects of incorrect geometry at contact surface on the coefficient are taken into account. The influences of pitch error and flatness deviation at the nut-loaded surface are discussed. Finally, a simple equation for estimating the coefficient is presented, where the major factors influencing scatter in clamping force are considered.