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info Overview

Pick a metric coarse thread from M1 to M30 to see the spanner flat width, drill hole for tapping and nut height, per old JIS / DIN 934 and ISO 4032.

📘 How to Use

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

Bolt & Wrench Size Reference

build Spanner / Wrench
Old JIS / DIN 934
-- mm
architecture Drill Hole
-- mm
height Nut Height
-- mm

The large figures are hex nut values from the old JIS (annex) and the German DIN 934. Under ISO 4032 and the current JIS, the width across flats differs by 1-2 mm for M10, M12, M14 and M22 (bolt heads too), and nuts from M5 up are slightly taller. From M1.6 up, the ISO value is shown underneath, so check it against the nut or bolt in your hand.

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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

  • One Click per Size: Click a bolt size (from M1 to M30) to 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.
  • Two Standards Side by Side: The large figures follow the old JIS and German DIN 934 hex nut tables. The ISO 4032 value, which the current JIS also uses, is shown underneath.
  • Improve Efficiency: No more searching through physical charts or guessing sizes. Pick a bolt size and the spanner size, drill diameter and nut height appear together.

🧐 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.

Q. Is an M10 nut 16 mm or 17 mm across flats?

A. Both exist. DIN 934 and the old JIS use 17 mm, while ISO 4032 and the current JIS use 16 mm. Only four sizes differ in width across flats: M10 (17/16 mm), M12 (19/18 mm), M14 (22/21 mm) and M22 (32/34 mm). If your wrench does not fit, try the other size.

📚 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.