1.2   NAMING

1.3   TYPES
Screws and nuts are used to affix and hold unions of removable elements, so if the helix of the nut is external, it is a screw, and if it is internal, it is a nut.

The most important part of the screws and nuts is the thread.


It is named screw to a mechanic cylindrical element used to affix temporarily some pieces with others. Screws have a spiral groove carved in the surface of a cylinder.


Head: The head is the widest part and able to hold the screw or to apply a rotatory movement with the help of suitable tools. Heads can be cylindrical, hexagonal, squared...

Neck: It is the part that is not threaded between the head and the thread.

 Thread: It is the part with spiral groove.

 Nut must always have the same features than the screw with which is affixed, so it is normalized according to general systems of threads.

Thread of a screw:

It is the distance between the crests of two following threads. Distance from one crest to the following, measured in parallel to the shaft.

External thread: thread in the external surface of a cylinder.

Internal thread: thread carved in the interior of a piece.

Internal diameter: longest diameter of an internal and an external thread.

Nucleus diameter: shortesst diameter of an internal and external thread.

Diameter of the sides (or average): diameter of an imaginary cylinder that goes through the crests in the point in which the width of these is equal to the space between themselves.

Movement: distance that the screw will move forward in a rotation. For a simple thread screw it is equal to the walkway, for a double thread, it is twice the walkway, and so and so forth. 


Basically, in screw naming there are included the following information:

      -          kind of screw according to its head

      -          name of the nut: M16 X 2

      -          length

      -          norm that defines it


Hexagonal screw d1=M16 x 2 DIN 934 – m8

                                          ↓                      Resistance (quality)

                           Naming of the thread

M-16  it is a 16mm external diameter thread, and the nut corresponding to it has 24mm from side to side.


  •  Hexagonal head screw

Union of two pieces with great torque.


          -        DIN: 532, 558, 601, 931, 933, 960, 961, 6914, 7964

          -        UNE-EN: 24015

          -        UNE-EN ISO

          -        4014, 4016, 4017, 4018, 5876, 8765

  • Hexagonal head screw with collar

Thanks to the collar that this screw has, there is no need of washers between the head and the piece to be united.


          -        UNE-EN: 1662, 1665, 14219

  •  Hexagonal head screw with pivot

Thanks to a passer, the piece is immobilized with great torque.


          -        DIN: 560, 561

  • Hexagonal head screw with sharp point

Also named prisioner screw because affixes pieces without them being able to move.

  • Grooved-head screws

In a hazelnut-headed it is posible to hide the head without a great torque.


          -        DIN: 63, 64, 68, 84, 85, 86, 87, 88, 91, 404, 920, 921, 922, 923, 925, 963, 964, 7969

          -        UNE-EN ISO: 1207, 1580, 2009, 2010

  • Screws with crossed slot head

In a hazelnut-headed it is posible to hide the head without a great torque.


          -        DIN: 966, 7985, 7986, 7987, 7988

          -        UNE-EN ISO: 7045,7046, 7047, 7048

  • Screw with prisioner head

A drill is needed to immobilize the screw without screwing.


          -         DIN: 604, 607, 792

  • Squared-neck screws

A drill is needed to immobilize the screw without screwing.


          -          DIN: 603, 605, 608

  • Hammer-head screw

Machinery fixation by T-shaped slots.


          -          DIN: 138, 188, 251

          -         UNE: 1721

  • Rounded-head screw

Manual assembleis and dismantlings.


          -         DIN: 434, 435, 563

  • Butterfly screw

For pieces that are assembled and dismantled frecuently.


          -         DIN: 314, 316

  • Autoscrewing screws for sheets

Thread is carried out in the screw when introducing this one in the metal sheet of little thickness or of soft material.


          -         DIN: 6901, 7513, 7516, 7971, 7972, 7973, 7974, 7976, 7978, 7879, 7981, 7982, 7983

          -         UNE: 1706, 17010, 17011, 17017

          -         UNE-EN ISO: 1479, 1481, 1482, 1483, 7049, 7050, 7051, 10510, 14585, 14586, 14587, 15480, 15481, 15482, 15483

  • Lag-screw

Thread is carried out in the screw when introducing this one in wooden


          -         DIN: 95, 96, 97, 570, 571, 7995, 7996, 7997

          -         UNE: 17023, 17024, 17025, 17027, 17028, 17094


For affixing screws suitably wrenches are needed. Because of this, some of these wrenches  are showed bellow:




Classicgear joint combination ratchet wrench;  is able to tihgten screws that other wrenches are not capable of due to the special design of its head, which allows it to spin until 90º adapting to areas difficult to access (see upper image).

As it has 72 teeth, with only 5º it is able to do accurate torques in areas with difficult movement.



Double offset ring wrench has its mouths in an 75º angle. This make it easier to access areas where the screw is under the surface surrounding.

1.3.3        OPEN-END WRENCHES


Open-end wrenches of open mouth are used to access to screws that are screwed and that a close mouth wrench is not able to access. For example, when a nut is in middle of an installed pipe which has no access from any of its sides.



Thanks to a U-turn tab, the reversible reversible combination ratchet wrench  makes it possible to tight in extremely reduced spaces where simple wrenches have not enough space. In addition, it has its mouths in 15º angle to make the torque easier.

Apart from these wrenches, there are many other models here.