FASTENERS (SPECIAL)

Figure 2-5.—Sectional view of rivnut showing head and end designs. Hi-shear rivets are identified by code numbers similar to the solid rivets. The size of the rivet is measured in increments of thirty-seconds of an inch for the diameter and sixteenths of an inch for the grip length. For example, an NAS 1055-5-7 rivet would be a hi-shear rivet with a countersunk head. Its diameter would be 5/32 of an inch and its maximum grip length would be 7/16 of an inch. The collars are identified by a basic code number and a dash number that correspond to the diameter of the rivet. An A before the dash number indicates an aluminum alloy collar. The NAS528-A5 collar would be used on a 5/32-inch-diameter rivet pin. Repair procedures involving the installation or replacement of hi-shear rivets generally specify the collar to be used. Rivnuts The rivnut is a hollow rivet made of 6063 aluminum alloy, counterbored and threaded on the inside. They are manufactured in two head styles, flat and countersunk, and in two shank designs, open and closed ends. See figure 2-5. Each of these rivets is available in three sizes: 6-32, 8-32, and 10-32. These numbers indicate the nominal diameter and the actual number of threads per inch of the machine screw that fits into the rivnut. Open-end rivnuts are the most widely used, and are recommended in preference to the closed-end type. However, in sealed flotation or pressurized compartments, the closed-end rivnut must be used. FASTENERS (SPECIAL) Fasteners on aircraft are designed for many different functions. Some are made for high-strength requirements, while others are designed for easy installation and removal. Lock-Bolt Fasteners Lock-bolt fasteners are designed to meet high-strength requirements. Used in many structural applications, their shear and tensile strengths equal or exceed the requirements of AN and NAS bolts. The lock-bolt pin, shown in view A of figure 2-6, consists of a pin and collar. It is available in two head styles: protruding and countersunk. Pin retention is accomplished by swaging the collar into the locking grooves on the pin. The blind lock bolt, shown in view B of figure 2-6, is similar to the self-plugging rivet shown in figure 2-3. It features a positive mechanical leek for pin retention. Hi-Lok Fasteners The hi-lok fastener, shown in figure 2-7, com- bines the features of a rivet and a bolt and is used for high-strength, interference-free fit of primary structures. The hi-lok fastener consists of a threaded pin and threaded locking collar. The pins are made of Figure 2-6.—Lock bolts. 2-4