Position the panel or plate on the aircraft before securing it in place. The spring riveted to the structural member enters the hollow center of the stud, which is retained in the plate or panel. Then, when the stud is turned about one-fourth turn, the curved jaws of the stud slip over the spring and compress it. The resulting tension locks the stud in place, thereby securing the panel or plate. Q5-6. What are the three most common types of turnlock fasteners? RIVETS LEARNING OBJECTIVE: Identify the solid rivets, blind rivets, and rivnuts commonly used in aircraft construction. There are hundreds of thousands of rivets in the airframe of a modern aircraft. This is an indication of how important rivets are in the construction of aircraft. A glance at any aircraft will disclose the thousands of rivets in the outer skin alone. In addition to being used in the skin, rivets are used in joining spar and rib sections. They are also used for securing fittings to various parts of the aircraft, and for fastening bracing members and other parts together. Rivets that are satisfactory for one part of the aircraft are often unsatisfactory for another part. Two of the major types of rivets used in aircraft construction are the solid rivet and the blind rivet. The solid rivet must be driven with a bucking bar. The blind rivet is installed when a bucking bar cannot be used. SOLID RIVETS Solid rivets are classified by their head shape, size, and the material from which they are manufactured. Rivet head shapes and their identifying code numbers are shown in figure 5-13. The prefix MS identifies hardware under the control of the Department of Defense and that the item conforms to military standards. The prefix AN identifies specifications that are developed and issued under joint authority of the Air Force and the Navy. Solid rivets have five different head shapes. They are the round head, flat head, countersunk head, brazier head, and universal head rivets. Round Head Rivets Round head rivets are used on internal structures where strength is the major factor and streamlining is not important. Flat Head Rivets Flat head rivets, like round head rivets, are used in the assembly of internal structures where maximum strength is required. They are used where interference of nearby members does not permit the use of round head rivets. Countersunk Head Rivets Countersunk head rivets, often referred to as flush rivets, are used where streamlining is important. On combat aircraft practically all external surfaces are flush riveted. Countersunk head rivets are obtainable with heads having an inclined angle of 78 and 100 degrees. The 100-degree angle rivet is the most commonly used type. Brazier Head Rivets Brazier head rivets offer only slight resistance to the airflow and are used frequently on external surfaces, especially on noncombat-type aircraft. Universal Head Rivets Universal head rivets are similar to brazier head rivets. They should be used in place of all other protruding-head  rivets  when  existing  stocks  are depleted. BLIND RIVETS There are many places on an aircraft where access to both sides of a riveted structural part is impossible. When attaching many nonstructural parts, the full strength of solid-shank rivets is not necessary and their use adds extra weight. For use in such places, rivets have been designed that can be formed from the outside. They are lighter than solid-shank rivets but are amply strong. Such rivets are referred to as blind rivets 5-10 ANF0513 MS20470 UNIVERSAL AN 430 ROUND AN 456 BRAZIER MS20426 COUNTER- SUNK AN 442 FLAT Figure 5-13.—Rivet head shapes and code numbers.