the connection between a coupling 35 and a sucker rod 36 requires the application of high torque of an undetermined level without marring the surface of the coupling 35 the amount of torque required is dependent upon the forces used in the previous engagement the adhesives employed and indeterminate factors arising from long term use such as corrosion mechanical distortion or other factors the most critical parameter is the gripping force applied to the surface of the coupling 35 since the torque wrench can be operated at considerable mechanical advantage with the lever arm that is used however it can be shown that even in the least favorable case that is a one inch u201c slimhole u201d coupling a gripping force of 169 680 pounds is provided at 3000 psi pressure while a gripping force of 282 800 pounds is provided at 5000 psi hydraulic pressure this is based on the practical example of gripper heads each having 2 50 in 2 contact surface area there being six such contact arcs there are 12 0 in 2 of total head surface contact area for six inch hydraulic cylinders the individual piston areas are 28 28 in 2 giving a total piston driving area of 56 56 in 2 leading to the calculations of 169 680 pounds and 282 800 pounds given above for.