M20 Bolt Size and Thread Specifications
Quick answer
M20 bolts use 20mm major diameter with 2.5mm coarse pitch and a 17.5mm tap drill.
They are common in structural steel, towers, and heavy machinery.
Use the chart below and reference screw anatomy when you must confirm grip and thread length.
M20 is standard in steel construction and large machines for anchor-style and high-strength joints. Match structural specifications for grade and torque. Spanish reference: perno M20. For tap drill size, thread types, and thread identifier workflows, pair this page with tools as you verify threads.
Specifications
| Specification | Value |
|---|---|
| Nominal diameter | 20 mm |
| Standard pitch (coarse) | 2.5 mm |
| Fine pitch | 1.5 mm or 2.0 mm |
| Tap drill size | 17.5 mm |
| Closest imperial equivalent | 3/4-10 |
Hex head size
| Bolt size | Hex head size |
|---|---|
| M20 | 30 mm |
Common uses
Steel structures, machinery bases, medium anchor bolts, and heavy assemblies. Cross-check loads with the bolt size chart and screw size conversion when you mix metric and inch bins.
Related tools
Related charts
M20 vs M18 bolt size
Shank diameter and pitch set tap drill, hex key, and strength for each ISO size. Compare values in the tables above with the M18 bolt size page when you resize hardware.
Use the bolt size chart when you compare hex and shank columns across sizes.
Metric vs UNC thread size
Metric threads list diameter in millimeters and pitch in millimeters per thread; UNC lists nominal inch diameter and threads per inch. They are not interchangeable—taps, dies, and gauges differ.
Read metric vs unc thread context when series labels are unclear.
Use screw size conversion when you must match stocked parts.
M20 specifications and tools
How to choose the right bolt size
Choosing the correct bolt size depends on load, material, and thread type. Larger diameters increase strength, while thread pitch affects holding force.
Use the bolt size chart to compare shank and hex dimensions before you standardize hardware.
Use tap drill size guidance when you plan tapped holes.
Use the thread identifier when stamped sizes are missing.
FAQ
What is the standard pitch for an M20 bolt?
The common coarse pitch for M20 is 2.5 mm. Fine pitch options include 1.5 mm or 2.0 mm where specified.
What drill size should be used for tapping M20 threads?
For M20 x 2.5 coarse thread, use approximately a 17.5 mm tap drill. Use our Tap Drill Calculator for other pitches.
What imperial fastener is closest to M20?
3/4-10 is a practical reference for comparing M20 to inch hardware; verify fit for your application.