The safety joint provides quick release of the test string if the string below the packer becomes stuck. The toolstring and downhole gauges above the safety joint can then be recovered; the lower stuck portion can be retrieved by either fishing over the OD of the box section or by reengaging the pin section into the box section.

The coarse thread of the safety joint that carries the string load facilitates disengaging and reengaging. The safety joint is typically positioned on top of the packer and made up to the same torque as the other tools in the string. Left-hand torque is used to disengage the safety joint.

The breakout torque is controlled by shear pins. An adjusting ring prevents right-hand torque from acting on the shear pins. The safety joint can be reengaged by applying weight and rotating slowly to the right. The knurled, beveled ends of the adjusting ring provide high breakout torque during a fishing operation.