MAY 2015 Chapter 20 Standard Practices Page 20.5
20-30 Torque Requirements (continued)
WARNING
Two threads minimum must be exposed beyond nut on any
installation to insure proper locking of fastener. Four threads
maximum may be exposed. More than four threads exposed
may allow nut to seat against bolt shank, resulting in insufficient
joint clamping.
CAUTION
Never substitute AN bolts for NAS bolts. NAS bolts have higher
tensile strength.
E. Torque Requirements
1. Bolt and nut are to be clean and dry except when assembly procedure specifies anti-
seize or thread-locking compound.
2. If chattering or jerking occurs, disassemble and re-torque fastener.
3. If special adapters which change effective length of torque wrench are used, final
torque value must be calculated using formulas in Figures 20-1 and 20-2.
4. Proper thread engagement requires 2-4 threads beyond primary self-locking nut (palnuts
excepted).
5. Torque wrenches must be calibrated annually, when dropped, or when a calibration
error is suspected.
Any self-locking nut whose drag has deteriorated appreciably must be replaced. Damaged
hardware must be replaced.
20-31 Torque Stripe
WARNING
Refer to appropriate Material Safety Data Sheet (MSDS) and
take necessary safety precautions when working in proximity to
hazardous materials.
Refer to Figure 5-1. Lacquer-paint Torque Seal® is applied to all critical fasteners after
palnut installation in a stripe ("torque stripe") extending from the fastener's exposed
threads across both nuts and onto the component. Subsequent rotation of the nut or bolt
can be detected visually. Position torque stripes for maximum visibility during preflight
inspections. Approved Torque Seal® is listed in § 20-74.
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