Prevailing Torque Values Chart for Metric Lock Nuts to show prevailing-on torque and prevailing-off torque values according to ISO 2320 : 2008 "Prevailing torque type steel nuts - Mechanical and performance properties" standard.
Some important notes from ISO 2320 standard:
- ISO 2320 specifies performance parameters of lock nuts when tested at an ambient temperature range of 10 °C to 35 °C.
- ISO 2320 applies to prevailing torque all metal type nuts (lock nut with metal insert) and prevailing torque non-metallic insert (lock nut with nylon insert) type nuts
- ISO 2320 applies to lock nuts with metal inserts within the temperature range of −50 °C to +150 °C.
- ISO 2320 applies to lock nuts with nylon inserts within the temperature range of −50 °C to +120 °C.
- ISO 2320 applies to nominal thread diameters up to and including M39 with triangular ISO thread and mechanical properties according to ISO 898-2.
Note 1: Prevailing torque performance decreases as number of reuses; the user should take into account the effects of the reduced performance before any reuse.
Note 2: Off torque values given above are required values according to ISO 2320 under laboratory acceptance test conditions. Performance for lock nuts may vary in normal use.
Alloy Steel: A ferrous (or iron-based) alloy that contains appreciable concentrations of alloying elements (other than C and residual amounts of Mn, Si, S and P). These alloying elements are usually added to improve mechanical and corrosion resistance properties.
Prevailing-On torque: Torque to rotate the nut on its mating externally threaded component with no clamp force
Prevailing-Off Torque: Torque to rotate after backing off the nut until the removal of the clamp force in the externally threaded component.
Prevailing torque type nut: Nut which is not free-running on a mating thread and has a resistance to rotation independent of clamping or compression forces.