There are two types of micro-screw mechanisms that look very similar but do have subtle differences. They are called the Triovis and Spirofin fine adjustment . The micro-screw mechanisms of either the Triovis and Spirofin systems are located within the movable stud carrier or compensating block which is located at the end of the balance cock. The compensation block houses the spring stud and its setscrew as well as the fine adjustment micro-screw. The movable compensation block allows rotation of the spring stud about the balance spring enabling in-beat adjustment. The micro-screw mechanism allows "micro-rotation" of the regulator ring about the balance spring enabling rate adjustment. Even though the Triovis and Spirofin systems both incorporate these similar features, the subtle difference between the two is how the micro-rotation of the regulating ring is achieved. The Spirofin fine adjustment mechanism is comprised of the micro-screw, regulator ring and carrier , Spirofin ring and the regulator housing . The Spirofin ring is housed (or sandwiched) between the regulator housing and the regulator ring. A tab is attached to the Spirofin ring, which protrudes out towards the micro-screw and is moved by the turning of the micro-screw. The motion of the tab rotates the Spirofin ring.
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The surface friction between the Spirofin ring and the regulator ring causes the regulator ring to rotate with the Spirofin ring. This system relies on the coefficient of friction between the ring's surfaces for the transmission of motion and therefore occasional slippage between the two surfaces and back-lash could be an issue during adjustment. The Triovis fine adjustment mechanism utilizes a worm gear type mechanism to rotate the regulating ring. The micro-screw acts like the worm which mates with teeth of the regulating ring. Most worm gear drive systems are used for speed reduction and the Triovis fine adjustment system is no different. One unit turn of the micro screw will produce a fraction of a unit turn (or rotation) of the regulator ring . The regulator ring sits under the compensation block's ring. The micro-screw and spring stud set screw is housed within the compensation block . One of the main benefit of this mechanism is that it provides a very positive means of transmitting motion to the regulating ring with the addition benefit of minimizing back-lash with-in the mechanism You can see a Triovis fine adjustment in Horologium's "THOSE WONDERFUL PIGUET CHRONOGRAPHS PART 2" and a Spirofin in Horologium's "TWEAKING THE MARK XII: PART 2.2. In Walt's "TWEAKING THE MARK XII: PART 2.2., he mistakenly calls the Spirofin fine adjustment a Triovis fine adjustment.