Abstract: A self-sealing, self-locking nut in which the nut body includes an annular recess within which there is located an annular member of resilient sealing and locking material, such as a fluoroplastic, and compression-retention means integral with the nut body and including a radially inward extension of the clamping surface of the nut body, the extension being located beneath the annular member of resilient sealing and locking material and below the clamping surface such that upon engaging the fastener with a complementary threaded element and tightening the clamping surface extension against a workpiece, axial clamping forces tend to move the extension upwardly toward the remainder of the clamping surface, thereby essentially completely confining the annular member within the nut body and compressing the annular member axially while contracting the inside diameter of the annular member to establish a seal along the complementary threaded element and a prevailing-torque lock between the nut body and the compleme