Figure 4-99.  NACA riveting method.  Figure 4-100.  Assorted fasteners. Rivet factory head Shop head formed in countersink head or shank side. The upsetting is started with light blows,  then the force increased and the gun or bar moved on the  shank end so as to form a head inside the countersink well.  If desired, the upset head may be shaved flush after driving.  If utilizing this method, it is important to reference the  manufacturer’s instructions for repair or replacement. Special purpose fasteners are designed for applications in  which fastener strength, ease of installation, or temperature  properties of the fastener require consideration. Solid shank  rivets have been the preferred construction method for metal  aircraft for many years because they fill up the hole, which  results in good load transfer, but they are not always ideal.  For example, the attachment of many nonstructural parts  (aircraft interior furnishings, flooring, deicing boots, etc.)  do not need the full strength of solid shank rivets. To install solid shank rivets, the aircraft technician must  have access to both sides of a riveted structure or structural  part. There are many places on an aircraft where this access  is impossible or where limited space does not permit the use of a bucking bar. In these instances, it is not possible to use  solid shank rivets, and special fasteners have been designed  that can be bucked from the front.  [Figure 4-100] There are  also areas of high loads, high fatigue, and bending on aircraft.  Although the shear loads of riveted joints are very good, the  tension, or clamp-up, loads are less than ideal.  Special purpose fasteners are sometimes lighter than solid  shank rivets, yet strong enough for their intended use. These  fasteners are manufactured by several corporations and  have unique characteristics that require special installation  tools, special installation procedures, and special removal  procedures. Because these fasteners are often inserted in  locations where one head, usually the shop head, cannot be  seen, they are called blind rivets or blind fasteners. Typically, the locking characteristics of a blind rivet are not  as good as a driven rivet. Therefore, blind rivets are usually  not used when driven rivets can be installed. Blind rivets  shall not be used:  NOTE: For metal repairs to the airframe, the use of blind  rivets must be specifically authorized by the airframe  manufacturer or approved by a representative of the Federal  Aviation Administration (FAA). The first blind fasteners were introduced in 1940 by the  Cherry Rivet Company (now Cherry$^{®}$ Aerospace), and the  aviation industry quickly adopted them. The past decades  have seen a proliferation of blind fastening systems based on  the original concept, which consists of a tubular rivet with  a fixed head and a hollow sleeve. Inserted within the rivet’s  core is a stem that is enlarged or serrated on its exposed end  when activated by a pulling-type rivet gun. The lower end  of the stem extends beyond the inner sheet of metal. This  portion contains a tapered joining portion and a blind head  that has a larger diameter than the stem or the sleeve of the  tubular rivet.  When the pulling force of the rivet gun forces the blind head  upward into the sleeve, its stem upsets or expands the lower  end of the sleeve into a tail. This presses the inner sheet  upward and closes any space that might have existed between  it and the outer sheet. Since the exposed head of the rivet is  held tightly against the outer sheet by the rivet gun, the sheets  of metal are clamped, or clinched, together.  Blind Rivets Special Purpose Fasteners 1.  In fluid-tight areas. 2.  On aircraft in air intake areas where rivet parts may  be ingested by the engine. 3.  On aircraft control surfaces, hinges, hinge brackets,  flight control actuating systems, wing attachment  fittings, landing gear fittings, on floats or amphibian  hulls below the water level, or other heavily stressed  locations on the aircraft. 4-47