with the head. A screw break-off shaver tool must be  used if a flush installation is required. The stem of the  newer Composi-Lok3$^{®}$ and OSI Bolt$^{®}$ break off flush. Tapered shank bolts, such as the Taper-Lok$^{®}$, are lightweight,  high strength shear or tension bolts. This bolt has a tapered  shank designed to provide an interference fit upon installation.  Tapered shank bolts can be identified by a round head (rather  than a screwdriver slot or wrench flats) and a threaded shank.  The Taper-Lok$^{®}$ is comprised of a tapered, conical-shank  fastener, installed into a precision tapered hole. The use of  tapered shank bolts is limited to special applications such as  high stress areas of fuel tanks. It is important that a tapered  bolt not be substituted for any other type of fastener in repairs.  It is equally as important not to substitute any other type of  fastener for a tapered bolt.  Tapered shank bolts look similar to Hi-Lok$^{®}$ bolts after  installation, but the tapered shank bolts do not have the hex  recess at the threaded end of the bolt. Tapered shank bolts  are installed in precision-reamed holes, with a controlled  interference fit. The interference fit compresses the material  around the hole that results in excellent load transfer, fatigue  resistance, and sealing. The collar used with the tapered shank  bolts has a captive washer, and no extra washers are required.  New tapered shank bolt installation or rework of tapered shank  bolt holes needs to be accomplished by trained personnel.  Properly installed, these bolts become tightly wedged and do  not turn while torque is applied to the nut.  is completed.  [Figure 4-113]  Often used for parts that are  removed frequently, the rivet nut is available in two types:  countersunk or flat head. Installed by crimping from one side,  the rivet nut provides a threaded hole into which machine  screws can be installed. Where a flush fit is required, the  countersink style can be used. Rivet nuts made of alloy steel  are used when increased tensile and shear strength is required. Flat head rivet nuts require only the proper size of hole while  flush installation can be made into either countersunk or  dimpled skin. Metal thinner than the rivet nut head requires  a dimple. The rivet nut size is selected according to the  thickness of the parent material and the size of screw to be  used. The part number identifies the type of rivet nut and the  maximum grip length. Recommended hole sizes are shown  in  Figure 4-114 . Correct installation requires good hole preparation, removal  of burrs, and holding the sheets in contact while heading.  Like any sheet metal fastener, a rivet nut should fit snugly  into its hole.  Common pull-type pop rivets, produced for non-aircraft- related applications, are not approved for use on certificated  aircraft structures or components. However, some homebuilt  noncertificated aircraft use pull-type rivets for their structure.  These types of rivets are typically made of aluminum and  can be installed with hand tools.  Sleeve bolts are used for similar purposes as tapered shank  bolts, but are easier to install. Sleeve bolts, such as the two  piece SLEEVbolt$^{®}$, consist of a tapered shank bolt in an  expandable sleeve. The sleeve is internally tapered and  externally straight. The sleeve bolt is installed in a standard  tolerance straight hole. During installation, the bolt is forced  into the sleeve. This action expands the sleeve which fills  the hole. It is easier to drill a straight tolerance hole than it  is to drill the tapered hole required for a tapered shank bolt. The rivet nut is a blind installed, internally-threaded rivet  invented in 1936 by the Goodrich Rubber Company for the  purpose of attaching a rubber aircraft wing deicer extrusion  to the leading edge of the wing. The original rivet nut is the  Rivnut$^{®}$ currently manufactured by Bollhoff Rivnut Inc. The  Rivnut$^{®}$ became widely used in the military and aerospace  markets because of its many design and assembly advantages.  Rivet nuts are used for the installation of fairings, trim, and  lightly loaded fittings that must be installed after an assembly  Figure 4-114.  Recommended hole sizes for rivet nut. Figure 4-113.  Rivet nut installation. Tapered Shank Bolt Hole Preparation Blind Fasteners (Nonstructural) Pop Rivets Sleeve Bolts Rivet Nut 4-56 5/32 #12 #2 .155–.157 .189–.193 .221–.226 No. 4 No. 6 No. 8 Rivnut ®  Size Drill Size Hole Tolerance