Understanding Metric Fasteners (2024)

FAQs

What does m6 M8 M10 mean? ›

Designation. A metric ISO screw thread is designated by the letter M followed by the value of the nominal diameter D (the maximum thread diameter) and the pitch P, both expressed in millimetres and separated by a dash or sometimes the multiplication sign, × (e.g. M8-1.25 or M8×1.25).

The "M" in the designation stands for "metric," indicating that the bolt follows the metric system of measurement. The first number, 8, represents the bolt's nominal diameter in millimeters, while the second number, 1.25, represents the distance between each thread crest.

Each size is denoted by the letter 'M' followed by a number. This number indicates the outer diameter of the thread, measured in millimetres. As an example, a hex bolt with a thread size of M8 would have an outer diameter of 8mm.

Metric threads are designated by the letter M followed by the nominal major diameter of the thread and the pitch in millimeters. For example M10 x 1.0 indicates that the major diameter of the thread is 10mm and the pitch is 1.0mm. The absence of a pitch value indicates that a coarse thread is specified.

Thread Diameter: M8: The "M" stands for metric, and "8" refers to the nominal diameter of the bolt's thread in millimeters. So, an M8 bolt has a thread diameter of 8mm. M10: Similarly, an M10 bolt has a thread diameter of 10mm. M12: An M12 bolt has a thread diameter of 12mm.

If the thread is specified simply as M6, it's a standard pitch. Standard pitch would be fully written as M6 x 1.0. Fine would be M6 x 0.8. Note, though, that the pitch varies with the thread diameter – so a standard M8 thread is M8 x 1.25 and a fine thread M8 x 1.0.

Standard metric screw dimensions are determined by the pitch and the major diameter, which as the illustration shows, is the largest diameter of the screw. Let's say it's 4mm, in which case it appears as M4 (the M means metric). Now let's say the pitch is 1mm. The size of your screw is M4 x 1mm.

First measure the diameter of the thread with a calliper. Using the conversion table below, you can determine the inch dimension as a metric dimension and convert it. By definition, one inch is 25.4 mm. The diameter therefore tells you whether the thread is metric or inch.

For nuts the size dimensions used are simply diameter and pitch. Here's an example metric bolt specification: M8-1.0 x 20. This bolt specification breaks down like this: The letter 'M' indicates that this bolt uses a metric thread. The number '8' refers to the nominal diameter of the bolt shaft in millimeters.

What is the difference between M10 and M10x1 25? ›

So, a thread labeled “M10” implies a coarse pitch by default. Any added pitch callout, like M10x1. 25, indicates a non-coarse pitch. This ISO standardization dramatically aids in reducing confusion and errors in the manufacturing process.

M8 is the designation for a metric (M) sized bolt or screw that is 8mm (8) in diameter. This is roughly equivalent to a 5/16 bolt or screw.

The M12 in the name refers to 12 millimetres. That's not the diameter of the bolt's head, though. It's the diameter of the bolt's thread and thus what you should be keeping in mind when measuring your hole. Other M-labelled bolts all follow the same system – an M16 refers to a bolt with a 16-millimetre diameter thread.

Coarse screws have a larger pitch than similarly-sized fine screws. A M12 x 1.75 x 85 screw, for instance, has threads every 1.75 mm (0.069 in). The second number, 1.75, indicates the pitch. The metric labeling system doesn't label coarse or fine screws, so you have to pay attention to the pitch.

Metric fasteners use thread pitch

It is expressed in millimetres. Metric fasteners are typically prefixed by an M, which makes them easily distinguishable from imperial fasteners. Thread patterns are classified as either coarse (longer) or fine (shorter) pitch.

Property Class 10.9 bolts and screws have a minimum tensile strength of 1040 MPa for all sizes. As you can see, they're slightly stronger than the nominal value in the property class designation. Property Class 10.9 bolts are considered high-strength parts. They're in the neighborhood of SAE J429 Grade 8 parts.