M13 Bolt Size and Thread Specifications
Quick answer
M13 bolts use 13mm major diameter with 1.75mm coarse pitch in reference tables.
They sit between M12 and M14 for some heavy equipment lines.
Use the tables below and screw size conversion when you swap metric for inch hardware.
M13 is uncommon compared with M12 or M14. Treat manufacturer drawings as authoritative for pitch and strength. Spanish reference: perno M13. For tap drill size, thread types, and thread identifier workflows, pair this page with tools as you verify threads.
Specifications
| Specification | Value |
|---|---|
| Nominal diameter | 13 mm |
| Standard pitch (coarse) | 1.75 mm |
| Fine pitch | 1.5 mm |
| Tap drill size | 11.2 mm |
| Closest imperial equivalent | 1/2-13 (approx.) |
Hex head size
| Bolt size | Hex head size |
|---|---|
| M13 | 20 mm |
Common uses
Equipment that explicitly lists M13 in service documentation. Cross-check loads with the bolt size chart and screw size conversion when you mix metric and inch bins.
Related tools
Related charts
M13 vs M14 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 M14 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.
M13 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 M13 bolt?
The common coarse pitch for M13 is 1.75 mm. Fine pitch is often 1.5 mm where specified.
What drill size should be used for tapping M13 threads?
For M13 x 1.75 coarse thread, use approximately a 11.2 mm tap drill. Use our Tap Drill Calculator for other pitches.
What imperial fastener is closest to M13?
1/2-13 (approx.) is a practical reference for comparing M13 to inch hardware; verify fit for your application.