APR 2019 Chapter 20 Standard Practices Page 20.5
20-30 Torque Requirements (continued)
E. Torque Requirements
CAUTION
Never substitute AN bolts for NAS bolts. NAS bolts have higher
tensile strength.
1. Any self-locking nut whose drag has deteriorated appreciably must be replaced.
Damaged hardware must be replaced.
2. Bolt and nut are to be clean and dry except when assembly procedure specifies
anti-seize or thread-locking compound.
3. If chattering or jerking occurs, disassemble and re-torque fastener.
4. 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.
5. Unless otherwise specified, proper thread engagement requires:
a. If palnut is not required, one to four threads exposed beyond primary nut.
b. If palnut is required, two to four threads exposed beyond primary nut.
c. For B526-8 screws, one to five threads exposed beyond primary nut.
WARNING
Proper thread engagement ensures proper locking of fastener.
Exceeding maximum thread exposure beyond primary nut
may allow nut to seat against unthreaded shank, resulting in
insufficient joint clamping.
6. Refer to Part A. Torque wrenches must be calibrated annually, when dropped, or
when a calibration error is suspected.
20-31 Torque Stripe
WARNING
Refer to Safety Data Sheet (SDS) and observe precautions
when working in proximity to hazardous materials.
Refer to Figure 5-1. Apply lacquer-paint Torque Seal® 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.
If, during inspection, the remaining torque stripe on a fastener is insufficient to determine
joint integrity, then remove accompanying palnut as required and apply specified torque
to fastener. If fastener moves, disassemble joint and inspect parts for damage such as
fretting, thread deformation, hole elongation, etc.; replace damaged parts. If fastener
does not move, install new palnut as required & standard torque per § 20-32. Torque
stripe fastener per § 20-31.
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