The invention relates to a threaded fastener. In particular, the invention relates to a threaded fastener such as a nut or a bolt. In an embodiment of the invention, a threaded fastener in the form of a nut (10) is disclosed. The nut comprises a main body portion (12); a lip portion (14) extending from the main body portion; and a recess (16) formed in the main body portion adjacent the lip portion. The recess is shaped to receive at least part of the deformable lip portion when a mating torque is applied to the fastener causing the deformable lip portion to deform. In this fashion, when the fastener is used to clamp two or more components together, such as flanges (20, 22) on adjacent pipe sections, the lip portion encounters a surface of the component that the fastener is being used to clamp against. As the fastener is torqued-up to a desired level, to provide a determined mating force, the lip portion is deformed into the recess in the main body portion.