The repair needs to be sanded, primed, and painted with an  approved paint system. A lightning protection mesh needs  to be applied if composite patches are used in an area that is  prone to lightning strikes. Many companies make specialty fasteners for composite  structures and several types of fasteners are commonly used:  threaded fasteners, lock bolts, blind bolts, blind rivets, and  specialty fasteners for soft structures, such as honeycomb  panels. The main differences between fasteners for metal  and composite structures are the materials and the footprint  diameter of nuts and collars.  Neither fiberglass nor Kevlar$^{®}$ fiber-reinforced composites  cause corrosion problems when used with most fastener  materials. Composites reinforced with carbon fibers,  however, are quite cathodic when used with materials, such  as aluminum or cadmium, the latter of which is a common  plating used on fasteners for corrosion protection. Titanium alloy Ti-6Al-4V is the most common alloy for  fasteners used with carbon fiber reinforced composite  structures. Austenitic stainless steels, superalloys (e.g.,  A286), multiphase alloys (e.g., MP35N or MP159), and  nickel alloys (e.g., alloy 718) also appear to be very  compatible with carbon fiber composites. The lockbolt incorporates a collar that is swaged into annular  grooves. It comes in two types: pull and stump. The pull- type is the most common, where a frangible pintail is used to  react the axial load during the swaging of the collar. When  the swaging load reaches a predetermined limit, the pintail  breaks away at the breakneck groove. The installation of  the Hi-Lok$^{®}$ and the pull-type Huck-Spin$^{®}$ lockbolt can be  performed by one technician from one side of the structure.  The stump-type lockbolt, on the other hand, requires support  on the head side of the fastener to react the swage operation.  This method is usually reserved for automated assembly of  detail structure in which access is not a problem. The adjustable sustain preload (ASP) fastening system  provides a simplified method of fastening composite,  soft core, metallic or other materials, which are sensitive  to fastener clamp-up or installation force conditions.  Clamping force can be infinitely adjustable within maximum  recommended torque limits and no further load is applied  during installation of the lock collar. The fastener is available  in two types. The ASP$^{®}$ has full shank and the 2ASP$^{®}$ has a  pilot type shank.  [Figures 7-76  and  7-77] The specific differences in these fasteners for composite  structure in contrast to metal structure are small. For the  Hi-Lok$^{®}$, material compatibility is the only issue; aluminum  collars are not recommended. Standard collars of A286,  303 stainless steel, and titanium alloy are normally used.  The Huck-Spin$^{®}$ lockbolt requires a hat-shaped collar that  incorporates a flange to spread the high bearing loads during  installation. The lockbolt pin designed for use in composite  structure has six annular grooves as opposed to five for metal  structure.  [Figures 7-79  and  7-80] Most composite primary structures for the aircraft industry  are fastened with Hi-Loks$^{®}$ (Hi-Shear Corp.) or Huck- Spin$^{®}$ lockbolts for permanent installations. The Hi-Lok$^{®}$  is a threaded fastener that incorporates a hex key in the  threaded end to react to the torque applied to the collar  during installation. The collar includes a frangible portion  that separates at a predetermined torque value.  [Figure 7-78] Eddie-Bolt$^{®}$ fasteners (Alcoa) are similar in design to Hi- Loks$^{®}$ and are a natural choice for carbon fiber composite  structures. The Eddie-Bolt$^{®}$ pin is designed with flutes in  the threaded portion, which allow a positive lock to be made  during installation using a specially designed mating nut or  collar. The mating nut has three lobes that serve as driving  ribs. During installation, at a predetermined preload, the lobes  Eddie-Bolt® Fasteners Hi-Lok® and Huck-Spin® Lockbolt Fasteners Fastener System for Sandwich Honeycomb  Structures (SPS Technologies Comp Tite) Fastener Materials  Corrosion Precautions Fasteners Used with Composite Laminates Step 8: Application of Finish Coat and Lightning Protection  Mesh Figure 7-76.  ASP fastener system.  7-46