or self-plugging because of the self-heading feature. Figure 5-14 shows a general type of blind rivet. RIVNUTS The rivnut is a hollow aluminum rivet that is counterbored and threaded on the inside. The rivet is installed with the aid of a special tool. Rivnuts are used primarily as a nut plate. They may be used as rivets in secondary structures such as instruments, brackets, and soundproofing materials. After rivnuts are installed, accessories can be fastened in place with screws. Rivnuts are manufactured in two head styles, countersunk and flat, and in two shank designs, open and closed ends. See figure 5-15. Open-end rivnuts are the most widely used. They are preferred in place of the closed-end type. However, in sealed flotation or pressurized compartments, the closed-end rivnut  must  be used. Further information concerning rivets may be found in  Aviation Structural Mechanic (H&S) 3 & 2, NAVEDTRA 12338. Q5-7. What are the two major types of rivets used in aircraft construction? Q5-8. What type of rivets are used where streamlining is important? MISCELLANEOUS FASTENERS LEARNING OBJECTIVE: Recognize the miscellaneous fastener used to fasten special purpose units. Some fasteners cannot be classified as rivets, turnlocks, or threaded fasteners. Included in this category are snap rings, turnbuckles, taper pins, flat head pins, and flexible connector/clamps. SNAP RINGS A snap ring is a ring of metal, either round or flat in cross section, that is tempered to have springlike action. This springlike action holds the snap ring firmly seated in a groove. The external types are designed to fit in a groove around the outside of a shaft or cylinder. The internal types fit in a groove inside a cylinder. A special type of pliers is made to install each type of snap ring. Snap rings may be reused as long as they retain their shape and springlike action. TURNBUCKLES A turnbuckle is a mechanical screw device consisting of two threaded terminals and a threaded barrel.  Figure  5-16  shows  a  typical  turnbuckle assembly. 5-11 ANF0514 LOCKING COLLAR NOTE SHEET GAP LOCKING COLLAR INSERTED (A) INSTALLED (B) Figure 5-14.—Self-plugging rivet (mechanical lock). ANF0515 COUNTERSUNK FLAT HEAD OPEN END CLOSED END CLOSED END OPEN END Figure 5-15.—Sectional view of rivnut showing head and end designs. ANF0516 L  (THREDS FLUSH WITH ENDS OF BARREL) BARREL SWAGING TERMINAL PIN EYE Figure 5-16.—Typical turnbuckle assembly.