Screws and nuts are used to fasten and fix joints of removable elements, therefore, if the helix of the thread is external, it is a screw and if it is internal, it is a nut.

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

A screw is a cylindrical mechanical element or operator used to temporarily fasten parts with each other. The screw has a helical groove carved into the surface of a cylinder.

PARTS OF A SCREW

• Head: The screw head is the widest part and this allows you to hold the screw or give it a rotating motion with the help of the right tools. This head can be cylindrical, hexagonal, square, ...
• Neck: This is the part of the screw that is unthreaded between the head and the thread.
• Thread: It is the part of the cylinder that has the helical groove.
  • Pitch: It is the distance between the ridges of two successive fillets. The distance from a point on a fillet to the corresponding point on the adjacent fillet, measured parallel to the axis.
  • External thread: This is a thread on the outer surface of a cylinder.
  • Internal thread: This is a thread carved into the inside of a piece.
  • Inner diameter: This is the largest diameter of an internal and external thread.
  • Core diameter: This is the smallest diameter of an internal or external thread.
  • Flank diameter (or middle): is the diameter of an imaginary cylinder that passes through the fillets at the point at which the width of the fillets is equal to the space between them.
  • Feed: it is the distance that the screw will advance relative to the nut is one rotation. For a single-threaded screw the feed is equal to the pitch, for a double-threaded screw, the feed is twice the pitch, and so on.

DESIGNATION

Basically, the following data are included in the designation of the screws:

• Screw type according to the shape of its head
• Thread Designation: M16 X 2
• Longitude
• Norm that defines it

Example:

Tornillo hexagonal d1=M16 x 2 DIN 934 – m8

Where:

• M16 is the thread designation
• And M8 Resistance (Quality)

Therefore, since M-16 is a thread with an outer diameter of 16mm, the nut that corresponds to that thread has 24mm between faces.

TYPES OF SCREWS AND SOME EXAMPLES OF WRENCHES

Hex Head Screw

Joining of pieces with great tightening.

STANDARDS:

• DIN: 532, 558, 601, 931, 933, 960, 961, 6914, 7964
• UNE-EN: 24015
• UNE-EN ISO 4014, 4016, 4017, 4018, 5876, 8765

Hex head screw with flange

With the flange that carries this screw, there is no need to use a washer between the screw head and the part to be joined.

STANDARDS

• UNE-EN: 1662, 1665, 14219

Hex Head Screw with Pivot

With the help of a pin, it immobilizes the workpiece with a large tightening

STANDARDS

• DIN: 560, 561

Hex head screw with pointed end

It is also called a grub screw because it joins the pieces preventing any type of movement

Slotted head screws

In a countersink it is possible to hide the head without the need for a large tightening.

 STANDARDS

• 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

Head screws with cruciform groove

In a countersink it is possible to hide the head without the need for a large tightening.

STANDARDS

• DIN: 966, 7985, 7986, 7987, 7988
• UNE-EN ISO: 7045,7046, 7047, 7048

Head screw with stud

A drill is needed to immobilize the screw without threading.

STANDARDS

• DIN: 604, 607, 792

Square neck screws

A drill is needed to immobilize the screw without threading.

STANDARDS

• DIN: 603, 605, 608

Screw with hammer head

Fastening machines by means of T-grooves.

STANDARDS

• DIN: 138, 188, 251
• UNE: 1721

Screw with rounded head

They are suitable for manual assembly and disassembly without the need for a large tightening.

STANDARDS

• DIN: 434, 435, 563

Thumbscrew

It is used for parts that are assembled and disassembled very frequently. It is used to make joints without great tightening.

STANDARDS

• DIN: 314, 316

Self-tapping screws for sheet metal

The thread is made by the screw itself when it is inserted into the thin metal sheet or soft material (plastic).

STANDARDS

• 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 bolts

The thread is made by the screw itself when it is inserted into the wood

STANDARDS

• DIN: 95, 96, 97, 570, 571, 7995, 7996, 7997
• UNE: 17023, 17024, 17025, 17027, 17028, 17094

WRENCHES

To fix the screws properly in every situation, wrenches are needed. Therefore, below are some of these keys and a possible example of use.

ARTICULATED RATCHET COMBINATION WRENCH

The articulated ratchet combination wrench is capable of tightening screws that other wrenches cannot due to the special design of its head, which allows it to rotate up to 90º adapting to hard-to-reach areas. (See image above).

As it has 72 teeth, with only 5º it allows precise tightening in areas with little space and mobility.

DOUBLE OFFSET RING WRENCH

The angled key has its mouths positioned at 75º. This makes it easier to access areas where the screw is lower than the surrounding surface.

OPEN-END FIXED WRENCH

Open-end fixed wrenches are mainly used to access screws that are threaded and that cannot be accessed with a closed-end wrench. For example, when a nut is located in the center of an installed pipe that has no access from either end (See image above).

REVERSIBLE RATCHET COMBINATION WRENCH     

Thanks to the U-turn tab of the reversible ratchet combination wrench, tightening is possible in extremely tight places where normal wrenches do not have enough space. In addition, it has its mouths positioned at 15º for easier tightening.