This mirror mount features a higher moment of inertia to maximize stiffness and reach thermal equilibrium characteristics faster. This is achieved by a hollow-frame design. Ideal for interference measurement or precision measurement. The mirror can be inserted from the back of the holder and fixed so that the reflecting surface of the mirror stops at the butt of the mirror frame with HX-25.4F-R. This ensures that the reflecting surface of the mirror is always aligned with the mounting center of the rod, even if the thickness of the mirror changes.