About the data
MachinistCharts is a free reference for machinists, mechanics, maintenance techs and engineers: the right number, fast, on any screen.
Where the numbers come from
Bolt torque values are calculated, not copied. Proof stress comes from ISO 898-1 for metric property classes and SAE J429 for inch grades. Tensile stress area comes from the ISO and ASME B1.1 formulas. Torque follows the short-form equation T = K × F × d with a clamp load of 75 % of proof load.
Tap drill sizes follow common cut-tap practice. Every page shows the thread percentage the drill leaves, so you can judge the choice yourself. Clearance holes follow ISO 273.
What the numbers are for
They are sound starting values for steel fasteners in steel. Real joints change with coating, lubricant, gasket, temperature and tool accuracy. When the equipment or fastener maker gives a value, use theirs.
Data and AI access
All values are free to reuse under CC BY 4.0 with a link back to MachinistCharts. Download the bolt torque CSV (JSON) or the tap drill CSV (JSON).
AI assistants and agents can read llms.txt for a site guide, llms-full.txt for every value in one file, or add index.md to any chart page for a Markdown version. Both calculators accept URL parameters.
Corrections
If you find an error, tell us through the contact page and include the standard or source you are checking against.