TM 55-1520-240-23-11-13STANDARD TORQUE LIMIT APPLICATION1-13This task provides standard torque limits for threadedfasteners, hose and tube coupling nuts, bulkheadfittings, and pipe thread fittings, and the minimumbreakaway torque values for determining reusability ofself-locking nuts. These standard torque values applyonly when special torque values are not specified inprocedures. General instructions for installation and fitof threaded fasteners are as follows:1.Thread shall not be in bearing when thickness ofsheet or fitting is 3/32 inch or less. If thickness ismore than 3/32 inch, a maximum of two threadsin bearing is permissible.2.In shear applications, thread shall not be inbearing regardless of material thickness.3.Washers are used for the following purposes:a.To compensate for differences in boltgrip length and material thickness due tomanufacturing tolerances, protective coating,and other surface variances.b.To distribute bearing load over a greater areato prevent damage to material under a bolthead or nut.c.To protect the material surface when a bolt ornut is tightened.d.Prevent galling of aluminum or other softmaterial when bolt or nut is tightened.e.To insulate dissimilar metals to preventcorrosion. The washer material should besimilar to the material on which it rests ratherthan the bolt or nut material. This insures thatit corrosion occurs, if will be between the boltand washer, which can be replaced.4.When nut-bolt assemblies are installed, the nutshall not engage the first incomplete thread nextto the bolt shank.5.Nuts are properly installed when all threads areengaged and the bolt chamfer extends thru thenut. When flat-end bolts are used, the threadedend must extend at least 1/32 inch thru the nut.6.Threads shall be clean and dry beforeinstallation. If threads are lubricated, torquelimits are reduced by 30 percent.7.The tightening sequence in multiple fittinginstallation is as follows:a.Finger tighten all bolts or nuts.b.Snug up opposite bolts or nuts all around.c.Tighten opposite bolts or nuts all around toproper torque. Do not torque adjacent boltsor nuts in sequence.8.All-metal self-locking nuts shall be replaced withnew identical parts at each installation. If newnuts are not available, all metal self-locking nutsmay be reused. The reused nuts must meet therequired minimum friction torque. See "FrictionTorque in Inch-Pounds for Threaded Fasteners"in this task.1-12
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