Figure 15-12: Acceptable and Unacce

Figure 15-12: Acceptable and Unacceptable Countersink AngleScrews installed into threaded (tapped) holes must have a minimum of three holding threads (see Section15.8.13 Thread EngagementThread engagement (dimension “A” in the following example) must be a minimum ofone times the nominal screw/bolt diameter for holes tapped in hard metals such as carbon steel, stainless steel,hard brass, etc. For holes tapped in aluminum and other soft metals, the thread engagement must be a minimumof one and one-half times the nominal screw/bolt diameter. In no case shall the screw/bolt bottom out in thetapped hole which would otherwise prevent the parts from being fastened together securely. .Care should be exercised during assembly to avoid damaging screw heads. Screw heads with damaged orburred slots are not acceptable. Take care in the selection of the proper size screwdriver or other tool (see Section15.8.15 Deformed Screw/Bolt HeadsThe conditions shown in Figure 15-22 can result from using a wrong orbadly worn tool, using the tool in an improper manner, and/or over torque the fastening device. In any event,these conditions are considered unacceptable and shall be cause for rejection. ).Nuts: The use of floating basket nuts is preferred when a countersunk hole is to be matched with a tapped hole(see Figure 15-13).Figure 15-13: Floating Basket Unit15.8.9 NutsHexagonal nuts are preferred for general usage. Square nuts may be used only when they are captive or floatingas part of a fastening device. Nuts should be sufficiently thick and strong so as not to fall before the bolt or screwfails in tension (see Figure 15-14).