Tightening torque to preload a UNC bolt
Tightening torque (thread + head friction), preload and equivalent stress for a UNC bolt (SAE grade system, US customary units).
Total tightening torque, M_A727 lb·in
Initial preload, F_i7237 lb
Thread friction torque, M_G374 lb·in
Thread friction torque, loosening, M_G--192 lb·in
Head face friction torque, M_WD353 lb·in
Equivalent stress, σₑ73 kpsi
Torsional stress, τ30 kpsi
Initial tensile stress, σᵢ51 kpsi
Proof strength, S_p85 kpsi
Major diameter, d0.5 in
Threads per inch, N13
Pitch, P77 1e-3 in
Pitch diameter, d_p0.45 in
Minor diameter, d_r0.4 in
Tensile stress area, A_t141.9 1e-3 in²
Method & references
- Tightening torque to preload a UNC bolt — SAE grade system.
The computation is a literal port of the original client-side JavaScript from /calculators/unc_2.htm. Results are verified equal to the original by an automated golden-master test. No formula has been re-derived or “improved”.