The flexibility of a clasp arm in removable partial dentures depends primarily on its length because the longer the clasp arm, the more it can flex under stress without permanent deformation. Length directly affects the clasp’s ability to engage the undercut of the abutment tooth while providing adequate retention and minimizing stress. While diameter, material, and shape influence flexibility, length has the most significant impact as it controls the clasp’s bending capacity. Increasing length reduces stiffness exponentially, making the clasp more resilient and comfortable for the patient.

Reference: Prosthodontics: Principles and Management Strategies, R. R. Shillingburg, 5th Edition.