Spanner / Wrench or Allen key sizes for metric thread bolts:

It may be a mechanical industry or a mechanical workshop or whatever, the use of fasteners are inevitable. It may be a large industry or a small workshop, if you don't prefer permanent joint (welding) then you should use fasteners. There are also many tools to handle these fasteners. Indeed the variety and type of fasteners are vast and it may be difficult to categorize even though there are common classifications which are mainly used. However there are certain fasteners which are standardised and used commonly around the world. Two of the most important fasteners we use around the world are bolts and screws. If you take a bolt then you should know that even that bolt also has many types like Allen bolt, Hexagonal bolt, etc. The tools used to handle these fasteners should be in proper size or else it will slip (removed from fastener) and will make injury. And so we have given the correct tool sizes for the most important and commonly used fasteners.

Spanner / Wrench or Allen key sizes for metric thread bolts:

Some of the most important fasteners are Allen bolts, Hexagonal bolts, CSK (Counter Sunk Bolt) and Grub screw / Set screw. Button head bolt also used for aesthetic looking.

1) We use Spanners or Wrenches (Spanners or Wrenches - two are same but name is different in different countries) for Hexagonal Bolt.

2) We use Allen key or Hex key (Allen keys or Hex keys - two are same but name is different in different countries) for Allen bolts, CSK bolts, Button Head bolts and Grub screw (Set screw).

We have given a table for your easy selection of proper size of tools. 

Caution:

  • Here we have given the tool size only for metric thread bolts.
  • We have not given the tools used for imperial thread or inches thread.
  • You should use the correct size of the tool mentioned in the table. Otherwise, it will slip (seperate from the tool) and causes mild or severe injury.

Note:

     If you are unfamiliar of these types of bolts and screws, you can refer the images given below the table for the proper identification of bolts and  screws.

Spanner / Wrench and Allen / Hex key sizes for metric thread bolts:

 

Size of bolts

Spanner/Wrench Size for Hex bolts

Allen/Hex key for Allen bolts

Allen/Hex key for CSK bolts

Allen/Hex key for Button head bolts

Allen /Hex key for set/ grub screw

M2

4

1.5

-

-

0.89

M3

5.5

2.5

2

2

1.5

M4

6-7

3

2.5

2.5

2

M5

8-9

4

3

3

2.5

M6

10-11

5

4

4

3

M8

12-13

6

5

5

4

Non standard

14-15

-

-

-

-

M10

16-17

8

6

6

5

M12

18-19

10

8

8

6

M14

20-22

12

10

10

6

Non standard

21-23

-

-

-

-

M16

24-27

14

10

10

8

M18

24-27

14

12

12

10

M20

30-32

17

12

12

10

M22

30-32

17

14

14

12

Note: The exact spanner size is the bold number. 

Reference:

If you don't know the exact bolt or unfamiliar with these bolts kindly refer the table below. 

Hexagonal Bolt:

Allen Bolt:

CSK Bolt:

 

Button Head Bolt:

 

Grub Screw or Set Screw:

 

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Basics:

  1. Fastener: Fastener is a device which joins two or more objects as a temporary joint. So we can easily remove the joints and again seperate these two objects.
  2. What is "M" in M5: M here denotes metric. So M5 means 5 mm (milli metre) metric thread. So when we mention the thread type of metric which is used in the bolt or screw we will mention the size of the bolt or screw prefixing M.   So we can say M3 Hex bolt, M3 Allen bolt, M3 nut, etc.
  3. Spanner / Wrench:  The tool used for tightening or loosening (fastening or removing) the hexagonal types of bolts or nuts is called spanner or wrench. The name spanner or wrench refers only one tool. But in some countries the tool is called spanner and in some countries it is called wrench. It has three types and they are  single ended spanner, double ended spanner and ring spanner.
  4. Allen key / Allen wrench/ Hex key: Allen bolt is a type of bolt which has cylindrical head having hexagonal bore in it. The tool used for handling this bolt is called Allen key or Hex key. Here Allen key or Hex key mentions the same tool.

    The head of the hexagonal bolt has six sides (hex - means six in Greek, gonia - means angle in Greek, bolt head has six sides and six angles) and so it is called hexagonal. But the head of the Allen bolt has only cylindrical shape. But it is called Allen Bolt. Why?

    It is believed that William G. Allen who invented this type of bolt and so it is called Allen bolt although independly others have invented.

  5. Exact Size of spanner or wrench:      Unlike allen or hex keys spanners often will come as double ended (both sides can be used but the size differs). So in one spanner we can tight two sizes of bolts. But we have given the exact size for a specific size of bolt in bold. So you should use the size of the bolded character in the table.    

    1) If you are interested to know about the metric bolt head sizes then follow the link below:

Metric Bolt Head Sizes

     2) If you are interested to know about the drill sizes for tapping  metric thread and BSP thread then follow the link below

Drill Sizes for Tapping Metric Threads and BSP Threads

               If you have any queries, kindly leave a comment below.

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