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A browser-based bolt & wrench size matcher tool. No data sent to server.

📘 How to Use

  1. Select a metric bolt size (e.g., M8) from the list.
  2. Instantly view the matching spanner size, drill hole diameter, and nut height.

Bolt & Wrench Size Matcher

build Spanner / Wrench
-- mm
architecture Drill Hole
-- mm
height Nut Height
-- mm

touch_app Select Bolt Size

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Article

Bolt & Wrench Size Finder｜Metric Spanner, Drill & Nut Chart

This online tool provides a quick and easy way to find the correct spanner/wrench size, tap drill size, and nut height for standard metric coarse thread bolts. It's an essential utility for engineers, mechanics, and DIY enthusiasts who need accurate measurements on the fly.

💡 Tool Overview

  • Instant Results: Simply click a bolt size (from M1 to M30) to instantly see the corresponding dimensions.
  • Three-in-One Data: Provides the required spanner (wrench) size, the correct drill bit size for tapping a hole, and the standard nut height.
  • Reliable Standard: All data is based on the common JIS (Japanese Industrial Standards) for metric coarse threads.
  • Improve Efficiency: No more searching through physical charts or guessing sizes. Get the exact measurements you need in seconds.

🧐 Frequently Asked Questions

Q. What do "M" and the number (e.g., M8) stand for?

A. "M" stands for "Metric," indicating the bolt uses the metric system. The number represents the nominal outer diameter of the thread in millimeters. For example, an M8 bolt has a nominal outer diameter of 8 mm.

Q. Is this chart applicable to all bolts?

A. This tool is specifically for metric coarse thread bolts, which are the most common type. The dimensions may not be accurate for fine thread bolts, imperial (inch-based) bolts, or bolts from other specialized standards. Always verify with the manufacturer's specifications when working on critical applications.

📚 Fun Facts about Bolt & Spanner Sizing

Did you ever wonder why an M8 bolt doesn't use an 8 mm wrench? The spanner size corresponds to the "width across flats" of the bolt head or nut, not the thread diameter. This is the distance between two parallel flat sides of the hexagon, which is standardized to be larger than the thread diameter to provide enough material for strength and grip.

Similarly, the "Drill Hole" size, often called the tap drill size, is crucial for creating internal threads. It's the diameter of the hole you need to drill before using a tap to cut the threads. If the hole is too large, the threads will be weak and shallow. If it's too small, the tap can bind and break during the threading process. This tool helps you select the perfect size to ensure strong, clean threads.