Torque & Fastener Matching Information

• In most race car chassis and aircraft airframe applications, the bolts used are loaded in shear. The torque values given in the NAS torque chart are adequate and appropriate for this type of usage.

• For aerospace bolt applications subjected to high tensile loadings and for aerospace nuts and bolts matched to fasteners of other grades and thread classes, refer to the following:
  • For applications requiring high installation torque values and using standard NAS bolts: achievable torque is dependent on plating, length of thread engagement, class of mating threads and lubricant (if any). 

• For maximum fatigue resistance and clamping force in the bolted assembly, we want to produce a level of installed tensile stress that is just below the yield strength of the bolt material (typically around 85% of the ultimate tensile strength). Achieving this ensures that the stresses encountered in the assembly/tightening process will be the most the bolt ever sees.

• At the yield point, the bolt will undergo "plastic" deformation (permanent stretch). Bolts for critical applications should be test-torqued to determine the point of measurable permanent stretch. As a rule, approximately 90% of this value will give the best performance in a bolted assembly.
  • Example: '93 INDY-LOLA ring gear bolts NAS 1307-4H- with light lubrication, these bolts stretch permanently on a consistent basis between 105 and 110 ft/lbs of installed torque. 90% of this value give an assembly torque of 95 ft/lbs

• The mating of aerospace spec (MS.NAS.AN) bolts and nuts to fasteners of other specifications and thread classes can cause problems. Nut splitting failures are primarily caused by overtorquing and/or thread class mismatches. Generally, NAS wrenching torque values should be reduced when aerospace nuts are matched with non-aerospace bolts or studs.

• Wrench torque values in the NAS nut tables below are achieved under laboratory conditions using aerospace spec bolts (Class 3 threads) of higher strength that the nuts they are mated to. THE TABLES DO NOT STATE, NOR SHOULD ONE INFER THAT THIS PERFORMANCE CAN BE DUPLICATED WITH OTHER TYPES OF FASTENERS AND/OR CLASSES OF THREADS.

• For applications requiring high clamping forces, 12 point nuts should be used whenever possible. Their greater thread contact area and higher rated strength make higher wrenching torque values possible.

• As a general rule, the wrenching torques values for aerospace spec nuts should be reduced approximately 25% as a starting point when these nuts are mated to non-aerospace bolts or studs.

Torque & Fastener Charts

• Recommended Torque Values for Nut/Bolt Combinations

• NAS Wrench Torque Values