NTA hydraulic bolt tensioner having a first chamber and a second chamber, a first hollow piston movable in the first chamber and partially extending into the second chamber, a second piston displaceable inside the first piston and movable in the second chamber, the second piston having connecting means for connecting with an end of a bolt, and a hydraulic fluid supply into the first chamber so that when hydraulic fluid pressure is applied to the first chamber, the first piston moves so that the first piston displaces the hydraulic fluid in the second chamber and moves the second piston to pull the end of the bolt.