STRENGTH LEVELS OF HEX NUTS VS HEX LOCK NUTS
Hex Nuts are typically manufactured to SAE J995 specifications. This SAE specification recognizes three strength levels of nuts - Grade 2, Grade 5 and Grade 8. The strength levels of these nuts are designed to be compatible with the corresponding grades of the cap screws. Locknuts are typically manufactured to Industrial Fastener Institute (IFI) 100/107 specifications. In order to differentiate between a free spinning nut and a nut that has prevailing torque (a wrench is required to run the nut up the threads of the cap screw) the IFI designated their nuts Grade A,Grade B and Grade C. These locknut grades are designed to be used on the same grades of cap screws as the free spinning nuts.
Locknut Hex Nut Maximum Grade of Cap Screw to be used with
Grade A Grade 2 Grade 2
Grade B Grade 5 Grade 5
Grade C Grade 8 Grade 8
The prevailing torque feature can be developed in several ways.
1. The side of the nut is punched to distort the threads.
2. The top bearing surface of the nut is punched to distort the threads.
3. A cone is added to the top of the nut and the threads in this area are distorted.
4. A nylon ring is added to the top of the nut.
5.A nylon patch is applied to the threads.
No matter what method is used to create the prevailing torque, the grade of nut must be compatible with the grade of the cap screw.
For thin styles of Nylon Insert Locknuts (NTU Series) Earnest Machine Products designate the nuts that are heat treated to the equivalent levels a Grade 8 Hex Jam nut as “Medium Carbon Steel Heat Treated”