Bolt torque and preload estimate calculator

Torque-factor preload estimate with supplied nut factor.

fasteners-bolt-preload.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	preloadN
	8333.33
	6666.67

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

preload budget8333.33 N✓ passes

BASELINE INPUTS

torque10 N*mdiameter6 mmnutFactor0.2

CALCULATED

preload8333.3 N

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Bolt torque and preload estimate
# Scope: Torque-factor preload estimate with supplied nut factor.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

torque = 10 N*m
diameter = 6 mm
nutFactor = 0.2

preload := torque/(nutFactor*diameter) [N]

check preload budget: preload <= 10000 N

scenario alternative: torque = 8 N*m

Calculated from your source · not saved

Baseline · Baseline

preload budget8333.33 N ✓ passes

alternative · alternative

preload budget6666.67 N ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

preload: preload = torque/(nutFactor*diameter) [N]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

torque: 10 N*m
diameter: 6 mm
nut factor: 0.2

Calculated

preload: 8333.33 N

Assumptions and limits

Torque-factor preload estimate with supplied nut factor.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Bolt torque and preload estimate. Inputs: bolt diameter; tightening torque; nut-factor interval. Outputs: preload range; torque sensitivity. Model scope: Explicit load paths, preload uncertainty and joint stiffness. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: bolt diameter, tightening torque, nut-factor interval
Outputs: preload range, torque sensitivity
Modes: calculate, compare, sweep
Drawing: Joint load diagram

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS