An athermal locking mechanism apparatus for large optic mounts is disclosed. The apparatus comprises at least one locking nut, at least one flexurized spring collet attached to a rigid base structure, a pivot shaft engaged with an optical yolk on a rotational axis of symmetry and a plurality of threads that joins the locking nuts with the flexurized spring collet The threads provide an increased level of a radial clamping force onto the pivot shaft, The interference generated between the locking nut and the spring collet causes all flexures to squeeze down onto the shaft, applying a purely symmetric radial force during the locking process. This eliminates any induced rotational torque and prevents the optical element from moving during the locking process after being properly aligned.