Abstract: A device for measuring the force exerted by a spring of a supporting grid on a fuel rod passing through the grid has an elongate body connected by two flexible blades that are parallel to the long direction to two respective beams insertable in a cell. At least one of the beams carries a force sensor designed to be pressed against the spring. A unit is slidable in the body along the body between a position in which it moves the beams apart while keeping them parallel to give them a spacing that corresponds to the nominal diameter of a fuel rod, and a position in which it allows the flexible blades to move the beams towards each other. The unit is movable at will between the two positions.