A nut fastener is provided for locking the nut to prevent inadvertent loosening of the nut. The nut fastener is particularly useful for tightening a wheel onto an axle. The nut fastener includes a nut, a collar and a retaining ring. The nut is unlocked by pushing on an engagement surface of the collar or by riding ratchet teeth over each other. When the collar is released, the collar locks against the nut to resist rotation of the nut.