Abstract: A three-roll thread gauge for measuring interior threads includes a fixed gauge roll and two movable gauge rolls. The motion of the two movable gauge rolls is constrained so that the interior angles of a triangle defined by the three gauge rolls are equal for each position of the first and second gauge rolls when the three gauge rolls are in engagement with an interior thread. The motion is constrained by reverse sine bars that limit the motion of first and second tables to which the first and second gauge rolls are attached.

Abstract: The invention is a gauge and method for measuring any circular object, but is most useful as a precision thread gauge for objects having either external or internal threads. A fixed gauge roll is supported in a stationary position. A first and second gauge rolls are supported so that the first and second gauge rolls simultaneously move with respect to the fixed gauge roll. The fixed gauge roll, first and second gauge roll together form a triangle. The interior angles of the triangle remain unchanged for every position of the three gauge rolls.

Abstract: The invention is a gauge and method for measuring any circular object, but is most useful as a precision thread gauge for objects having either external or internal threads. A fixed gauge roll is supported in a stationary position. A first and second gauge rolls are supported so that the first and second gauge rolls simultaneously move with respect to the fixed gauge roll. The fixed gauge roll, first and second gauge roll together form a triangle. The interior angles of the triangle remain unchanged for every position of the three gauge rolls.