Abstract: A method of applying a coating, such as a fluorocarbon barrier coating, to the threads of a fastener, particularly suitable for applying a coating to a female fastener having a threaded bore. The method includes forming a fluid suspension of the coating material, such as an unpolymerized fluorocarbon in an organic solvent, forming a drop of the coating material fluid suspension on the tip of an ultrasonic transducer and bringing the tip into proximity with the fastener threads, which are preferably preheated. The ultrasonic tip is then vibrated in the ultrasonic range, exploding the drop and coating the fastener threads with a fine mist of the fluid suspension. The fastener is then heated to vaporize the solvent and polymerize the coating material where the coating material is polymerizable. When coating female fasteners, the tip of the ultrasonic transducer is preferably lowered within the thread cylinder, adjacent the top thread.