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03 // Bidirectional STEM Calculators // ENGINEERINGT = K × F × d

Bolt Tightening Torque & Clamp Preload Calculator

The empirical Kellermann-Klein fastener equation relates tightening wrench torque T to axial bolt clamp preload F, nominal thread diameter d, and dimensionless nut friction factor K: T = K × F × d.

T = K × F × d
Pick which value you want to calculate (or type into any field):Solving for: T — Tightening Wrench Torque
Calculated

Installation torque in Newton-meters (switch unit for lb·ft)

0.550,000.00

Dimensionless torque coefficient (0.20 dry steel, 0.15 lubricated)

0.050.4
unit

Bolt tension clamping the joint in Newtons (switch to kN or lbf)

1002,000,000.00

Major thread diameter in meters (switch unit to mm or in)

0.0020.2
Calculated Result · Tightening Wrench Torque (T)
88N·m
Converted units:

Step-by-Step Calculation

01Canonical Law: T = K × F × d
02Given Inputs (Base Units): K = 0.2, F = 27,500 N, d = 0.016 m
03Solve for T (Tightening Wrench Torque): T = 88 N·m

The empirical Kellermann-Klein fastener equation relates tightening wrench torque T to axial bolt clamp preload F, nominal thread diameter d, and dimensionless nut friction factor K: T = K × F × d.

Real-World Reference Values

Dry Zinc-Plated Steel (K ≈ 0.20)M16 Class 8.8 @ 27.5 kN → 88 N·m

~90% of input torque is consumed by thread & head friction

Anti-Seize / Moly Lube (K ≈ 0.12 – 0.15)Reduces required torque by 25%–40%

Never use dry torque specs on lubricated threads

Target Preload (75% Proof Load)F ≈ 0.75 × A_t × σ_proof

VDI 2230 standard structural joint preload

20-Row Comparison Table

Tightening Wrench Torque (T) · Nut Friction Factor (K-Factor) (K)

Bolt Tightening Torque & Clamp Preload Calculator — Nut Friction Factor (K-Factor) → Tightening Wrench Torque
#Nut Friction Factor (K-Factor) (K)Tightening Wrench Torque (N·m)Δ %
010.05 22 N·m-75.00%
020.078947 34.7368 N·m-60.53%
030.107895 47.4737 N·m-46.05%
040.136842 60.2105 N·m-31.58%
050.165789 72.9474 N·m-17.11%
060.2 Current88 N·m0.00%
070.223684 98.4211 N·m+11.84%
080.252632 111.1579 N·m+26.32%
090.281579 123.8947 N·m+40.79%
100.310526 136.6316 N·m+55.26%
110.339474 149.3684 N·m+69.74%
120.368421 162.1053 N·m+84.21%
130.397368 174.8421 N·m+98.68%
140.426316 187.5789 N·m+113.16%
150.455263 200.3158 N·m+127.63%
160.484211 213.0526 N·m+142.11%
170.513158 225.7895 N·m+156.58%
180.542105 238.5263 N·m+171.05%
190.571053 251.2632 N·m+185.53%
200.6 264 N·m+200.00%
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Frequently Asked Questions

Why does lubricating a bolt without lowering wrench torque snap the fastener?+

Lubrication drops K from ~0.20 to ~0.12. Applying dry torque T to a lubricated bolt increases axial tension F = T / (Kd) by 67%, exceeding yield strength.

Can I enter bolt diameter d in millimeters (e.g., 16 mm for M16)?+

Yes. Switch the inline unit dropdown on d to Millimeters (mm) and on F to Kilonewtons (kN).

How much of the applied wrench torque actually stretches the bolt?+

Typically ~50% is lost to under-head friction and ~40% to thread flank friction; only ~10% produces elastic axial elongation.