Bolt Torque to Clamp Load
Short-form torque T = K * D * F with grade proof loads.
Example
You enter
- Grade SAE_5
- Diameter (in) 0.5
- Lubrication dry
- Preload fraction (0-1) 0.75
You get
- Clamp load 9,046 lb
- Torque (in-lb) 904.6
- Torque 75.4 ft-lb
- Nut factor K for this lubrication 0.2
Checked against published worked examples from: Fastenal.
Details, formula, and sources
Formula or tableT (in-lb) = K × D (in) × F (lb); ft-lb = T / 12, where K is the nut factor, D is bolt diameter, F is desired clamp load (= proof load × torque-tension factor). Proof loads per ASTM / SAE bolt-grade specifications.
Source and editionASTM A325 / A490 / SAE J429 by name.
Free accessASTM / SAE licensed; principles free in Machinery's Handbook (free at archive.org for older editions).
What governsEstimate. AHJ and licensed structural engineer govern.
API field namesgrade, diameter_in, lubrication, preload_fraction, F_lb, torque_in_lb, torque_ft_lb, K
- Nut factor K 0.20 dry / 0.15 lubricated unless user suppliesengineering practice
- Proof-load table data/construction/bolt-grades.jsonASTM / SAE by name