The invention provides a variable torque-rate test joint for the performance testing of rotary tools for threaded fasteners. In a typical test routine a nut is repeatedly tightened by the tool and after each tightening the nut must be released and run back to its start position. The invention provides a means for rapidly releasing the pressure on the tightened nut so that it can be run back quickly and easily. The variable joint is supported by a reaction surface that is the operative face of a piston and cylinder assembly seated on a shoulder fast to a shank of the threaded fastener. A hydraulic control is provided for the piston and cylinder assembly including means for hydraulically extending the piston from the cylinder to a fixed maximum extension which defines a test position of the reaction surface, and means for hydraulically retracting the piston back into the cylinder to remove the pressure from the nut at the end of the test. During tightening the piston is extended and preferably hydraulically locked.