An introduction to fasteners and its properties.

Work in progress!

This small guide was born from the need of researching and buying adequate fasteners for my Heacent Prusa i3. Quite a few screws weren’t sent by the manufacturer.

The curiosity to understand how the classification of fasteners workedAs I researched, I realized that the topic was a lot more complex than I anticipated and thus I decided that the best and most useful way to structure this guide was to use the full fastener classification begin with the Since I’m a beginner myself, I had to compile the content from respected sources, crediting them adequately.


Fasteners are classified according to each of its characteristics:

  1. Fastener type
  2. Head
  3. Material
  4. Size

The full fasteners notation condenses information about all characteristics of each fastener in a single line. For that reason it can be hard to understand it at first. Here are practical examples from BoltDepot (US added by me. The standard measuring system isn’t included.):

1. Fastener type

A broader category of classification using therms to succinctly describe the most notable characteristics of a given fastener.



It may include information about the measuring system used (imperial or metric):

2. Head

3. Material


4. Size



ISO metric fasteners

The M stands for metric and it’s a designation that identifies the basic sizing of washers, screws and nuts. The number following M is the measurement in millimetres of the outer diameter, in case of screws; or the inner diameter for nuts and washers.

Thread   Hex head
width    (mm)
M2       4
M2.5     5
M3       5.5
M4       7
M5       8
M6       10
M7       11
M8       13
M10      17
M12      19
M14      22
M16      24
M18      27
M20      30
M22      32
M24      36
M27      41
M30      46
M33      50
M36      55

The crews ISO metric nomenclature can also be accompanied by another value that describe the length of its threaded shaft. So, for example a screw identified as M3 x 20mm has the following measures:screw

The truth is that this identification system is a lot more complicated and full of parameters and although this is an interesting subject, it’s also absolutely unnecessary knowledge for assembling a 3D printer. If you’re interested, you can read more in this manual written by a fasteners shop.

Screws, bots and washers can also be classified by other characteristics – for instance, bolts can be classified by the shape of the head, the type of drive used to install them, if they are fully threaded or not and others. The most complete guide I found on this subject belongs to another fastener shop.

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