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About FastenerChart

A free engineering reference for fastener dimensions, published as a public resource. No accounts, no paywall, no signup.

What this is

FastenerChart publishes the dimensional and mechanical data engineers, machinists and mechanics look up constantly: tap drill sizes, clearance holes, torque specifications, thread geometry, and the wrench and hex key that fits each fastener. It covers 104 thread sizes across the metric coarse, metric fine, UNC and UNF series.

The reason it exists is narrow but real. All of this data is already published — in supplier PDFs that open sideways, forum posts from a decade ago, and chart pages that answer exactly one of the four questions you have while standing at a machine. Anyone working on a part needs the tap drill, the clearance hole, the torque figure and the socket size, and that has historically meant four browser tabs from four sources of varying reliability. FastenerChart puts the complete set on one page per thread.

Who publishes it

FastenerChart is an independently operated reference site. It is not affiliated with, endorsed by, or sponsored by any fastener manufacturer, tooling supplier, distributor or standards body. It has no commercial relationship with any organisation whose products or standards are referenced on the site.

The site is funded by display advertising. Advertising has no influence on the data — every value is computed from a published formula or a tabulated standard, and there is no mechanism by which an advertiser could alter a number. See our privacy policy for how advertising works here.

Corrections, questions and requests for additional coverage are welcome: get in touch.

Editorial approach

Three commitments govern what gets published:

Nothing is retyped from another chart. Values are computed from the governing standard at build time. Chart sites that copy from one another inherit each other's errors and have no way to answer where a number came from. Every figure here traces to a formula or a standard's table, both documented below.

Where a value is extrapolated rather than tabulated, the page says so. A handful of sizes are not listed in the standards we could source. Those pages carry a visible note explaining that the value follows the step pattern of its neighbours rather than presenting it as authoritative.

Where no correct answer exists, we print nothing. Thread sizes above roughly two inches have no standard inch drill equivalent. Those cells read "no standard inch drill" rather than reporting the nearest available size, which would be confidently wrong.

Every value on the site is checked at build time against a suite of assertions comparing sample figures to independently published references and enforcing catalogue-wide consistency. If a check fails, the site is not published.

Limitations

This is a reference, not an engineering authority. Torque figures in particular are general-engineering starting points calculated with standard assumptions about friction and preload; real joints vary enormously with lubrication, plating, material and geometry. For any safety-critical connection — a structural joint, a pressure vessel, an engine, a suspension component — use the specification supplied with the part, or one produced by a qualified engineer for your application. Nothing here is a substitute for that.

How the numbers are calculated

Every value is computed from the governing standard at build time, for all 104 thread sizes, using the formulas below.

Tap drill

Metric: drill = D − (P × %thread / 76.98). At 75% this collapses to the familiar D − P.
Imperial: drill = D − (0.01299 × %thread) / TPI. The result is then snapped up to the nearest standard number, letter or fractional drill.

Clearance holes

Metric values follow ISO 273 / ASME B18.2.8 close, medium and free series. Imperial values use the conventional major diameter plus 1/64", 1/32" and 1/16", snapped to a standard drill.

Thread geometry

Pitch diameter = D − 0.6495P (metric) or D − 0.6495/TPI (imperial).
Minor diameter = D − 1.0825P or D − 1.0825/TPI.
Tensile stress area = 0.7854 × (D − 0.9382P)² metric, 0.7854 × (D − 0.9743/TPI)² imperial.

Torque

T = K · D · F, with K = 0.20 for plain dry steel, and clamp load F set to 75% of proof load (proof load = stress area × proof strength for the grade). Proof strengths: 4.6 = 225 MPa, 8.8 = 580 MPa, 10.9 = 830 MPa, 12.9 = 970 MPa, A2-70 stainless = 450 MPa; SAE Grade 2 = 55 ksi (33 ksi above 3/4"), Grade 5 = 85 ksi (74 ksi above 1"), Grade 8 = 120 ksi.

Torque values computed this way land within a few percent of published manufacturer charts — but every published chart makes its own assumptions about friction and preload target, so small disagreements between sources are normal and expected. For a safety-critical joint, use the specification that comes with the part.

Corrections

If a number here is wrong, it is wrong for every size at once, because it comes from a formula. That is the point. Report it and it gets fixed globally.