Clamp force and its accuracy are investigated using torque, angle, gradient, and clamp force/elongation control. Phosphated, lightly oiled M14 and M10 bolts are tightened. A PowerMACS 4000 system with a QST62-350CT nutrunner is used in the experimental setup. An ultrasonic signal processing unit using a piezoelectric sensor fitted to the socket is used for signal generation and processing when evaluating clamp force. The ultrasonic clamp force control is based on a novel method for assuring correct echo and high repeatability measurements in the tightening system. Torque and angle are extracted from the tool control system. During the experiments a load cell is used to measure the clamp force in the joint. Combined head and thread friction is calculated at final torque and clamp force. The results show that the lowest scatter (3 s) in clamp force, approximately 2.9% can be obtained using ultrasonic clamp force control and the highest, approximately 18% when using torque control. The results are also compared to tightening factors described in VDI2230.