Mother (technology)

from Wikipedia, the free encyclopedia
From above: hex nut, square nut, cap nut, self-locking nut, wing nut

The nut (plural: nuts), sometimes also screw nut to distinguish it , is the counterpart of a screw or threaded bolt with an internal thread .

Nut and screw together form a screw connection .

Construction and assembly

Heavy bolt and nut 87 kg of a power plant - generator .

The screw nut is a hollow, usually low prismatic body, the inner surface of which is designed as an internal thread . The prismatic outer contour is used for connection with a wrench , with which the torque for tightening the nut is initiated. The most common are hex nuts. Their height is about half the width across flats . Nuts that are stuck due to corrosion can often be loosened with penetrating oil or by heating with a blowtorch . In extreme cases, the mother has a nut splitters split or a power cutter to be destroyed.

Material and manufacture

In addition to steel , non-ferrous metals ( brass , copper ), aluminum and plastics are also used to a lesser extent . In the case of steel nuts, the starting material today is usually high-alloy steel wire , which is hot-formed in several automated operations by forging and tempered by heat treatment . The thread is not cut, but rather formed without cutting .


The majority of nuts are standardized mass products . The non-standardized variants are mostly mass-produced products and can also be selected from catalogs .

The very large number of different designs can be found under

  • geometrical aspects (primarily the outer contour determined by the wrench to be used),
  • the possibly integrated measures against self-loosening,
  • any additional functions and
  • the intended special applications

sum up.

Many designs are available in different strength classes and with different levels of resistance to corrosion and chemical attack. Nuts of a higher strength class and with higher corrosion resistance are more expensive than standard designs.

Differentiation according to the outer contour

From left to right: Slotted hexagon nut, square nut (above), drive-in nut (below), cap nut, self-locking nut, castle nut

Hexagon nut

The hexagon nut is the most common shape today. It used to be the square nut .

Different nut height

  • Flat hexagon nut (0.5 × diameter high): ISO 4035, ISO 8675 (with fine thread), formerly DIN 439;
  • High hexagon nut (1.5 × diameter high): DIN 6330

Wrench sizes and dimensions can be found in the list of dimensions for metric hex nuts .

Slight modifications of the hexagonal nut, the tube nut , the castellated nut , the nut , the collar nut and the self-locking nut .

Square nut

Square nuts (see picture ) were often used in the past. The main reason was the easier production of square edges by manual forging and later waste-free punching.

Today square nuts can be found as insert nuts in injection-molded parts, or they are inserted into housing profiles (extruded aluminum profiles) in order to provide them with nut threads for screwing on other parts. A square nut is also the main part of a cage nut .

From left to right: wing nuts, hexagon nuts, blind rivet nuts, weld nuts with flange (for projection welding )

Wing nut

Wing nuts have a slightly conical outer contour to which two flat extensions - the wings - are attached radially. This means that they can be tightened (by hand) between thumb and forefinger without tools and (usually) released again.

Knurled nut

Knurled nuts can also be tightened and loosened without tools. The cylindrical outer surface is knurled , which improves contact with the fingers. It is also only moved with the fingers. In order to be able to hold the round nut better, the edge is roughened on the outside so that it is not so easy to slip when holding it. However, no large torques are possible, which is why it is more used in precision engineering .


In the case of a locknut , the cylindrical outer contour is provided with grooves . A suitable hook wrench is inserted into the incisions to tighten or loosen the nut.

Applications are shaft-hub connections and the connection of a roller bearing inner ring with the shaft. The locknut represents an axial stop between the hub / roller bearing ring and the shaft. It is usually provided with a fine thread .

Cross hole nut

A cross-hole nut has radial holes in its cylindrical outer contour into which pins attached to a hook wrench can engage.

  • Standard: DIN 1816

One variant is a nut with holes in the end faces of an otherwise cylindrical nut.

Differentiation according to measures against loosening

Two nuts of normal height countered against each other on a threaded rod

As a rule, a separate machine element is used to protect a nut against loosening .

Lock nut

The counter nut (also counter nut ) does not mean a design, but a second nut combined with a primary nut. The peculiarity of the shape is at most that a flat hexagon nut is often used as the lock nut . The nut and lock nut are twisted against each other, creating a frictional connection between them and the screw part below them. It must be ensured that the force between the nuts is significantly greater than the force acting on the primary nut. If locking is used to prevent the primary nut from loosening, screw on the flatter nut first, then the thicker nut. As a result, the thicker nut takes over most of the tensile force and the pressure between the nuts, which is supposed to prevent loosening, is greater.

"Countering" is one of the less effective measures against loosening. The cause is the slight elastic deformation of the nut and screw shaft, which act as "hard springs". This enables a quick and practically complete reduction in the clamping force due to creep , vibration or corrosion.

Castle nut

Castle nut with cotter pin

A castle nut is an extended hexagon nut that can be positively connected to the screw shaft with the help of a split pin or a focus needle to prevent it from turning. A corresponding transverse hole must be made in the shaft. The mother wears a radially slotted ring, a "crown". The split pin engages in one of these slots.

Self-locking nut with clamping part (plastic insert)

Self-locking mother

A self-locking nut (also called a stop nut ) secures it against loosening, without the need for an additional machine element, as with other screw locks, and without the screw shaft having to be machined.

A self-locking nut is a hexagon nut that is widened in the shape of a ring on one of the end faces and contains a ring made of plastic , usually made of polyamide, in an inner groove . This ring - called a clamping part according to the DIN standard - is plastically and elastically deformed when the screw passes through. The elastic component causes a radially acting force - fit securing against loosening of the nut. Because of the necessary deformation work, such a nut can usually not be screwed on by hand. Since the plastic ring wears when loosening and loses its locking effect, these nuts are disposable. Their reuse is a possible cause of failure.

The plastic lock can only develop its effect when the nut is completely on the screw connection. They usually have to be attached in such a way that at least two threads protrude.

Self-locking nuts with plastic rings are not suitable for high operating temperatures. So-called stover nuts are used (temperature range: −50 to +300 ° C), which are slightly out of round. The frictional connection is created by the elastic deformation of the nut metal.

Another technical version of the self-locking nut is the all-steel lock nut . A steel ring is mounted in the inner groove as a securing element. The securing element acts in the radial and axial direction and produces a uniform clamping effect over the entire circumference of a thread turn. The all-steel lock nut can be used multiple times. After screwing it on and off several times, the loosening torque is sufficiently high to prevent the nut from loosening from the male thread. The thermal load capacity reaches up to 1,000 ° C. The all-steel lock nut can be designed as a hexagon nut, as a hexagon nut with flange or as a special nut.

  • Standards: ISO 10511, old: DIN 985 (low form); ISO 7040, ISO 10512, old: DIN 982 , DIN 6924 (tall form), DIN EN ISO 7042 (hexagon nut, metal clamping part, standard thread), old: DIN 980, DIN EN ISO 10513 (hexagon nut, metal clamping part, fine thread), old : DIN 980, DIN EN ISO 1664 (hexagon nut with flange, metal clamping part, standard thread), DIN EN ISO 1667 (hexagon nut with flange, metal clamping part, fine thread), DIN EN ISO 2320 (mechanical and functional properties for steel hexagon nuts with clamping part)
Clamping nut with multiple screws (SVS)

Clamping nut

A clamping nut is a seldom used, usually very large nut. Several screws with a relatively small diameter are attached around the threaded hole, with which the nut loosely screwed onto the contact surface is fastened. A large wrench is not required and the tightening torque can be generated in steps distributed over the screws. The screws are tightened evenly while pressing against the contact surface.

Since the relatively many and small screws represent relatively "soft springs", a soft frictional connection can be established, and a tightened clamping nut is also considered to be a nut that is well secured against loosening.

Special nut shapes

With a large number of special nut shapes, special functions or applications are made possible. Some of them are industry specific. Some are connections of a nut to another component.

An example is the slotted nut, which sits on the thread like a normal nut and can be tightened or loosened with a slotted screwdriver through a slot across one of the end faces . The specialty of the cross nut bolt is that it cannot turn when it is in the recess.

Nuts for special functions

Pipe nut

A pipe nut is a particularly flat hexagon nut with a pipe thread according to DIN 431 . For example, it can be screwed onto a water pipe with a suitable thread.

Cap nut

Cap nuts M6 (DIN 1567) with 10 mm wrench size , brass and chrome-plated

A cap nut is a hexagon nut provided with a hat , in which the internal thread ends as a blind hole thread. The nut is closed on one side, and the screw end is protected from rust and dirt. In addition, the rounded hat prevents the risk of injury at the end of the screw.

  • Standard: DIN 1587; low form: DIN 917

Cap nuts are used, for example, on bicycles to fasten the wheel axles and as a counter nut to fasten Bowden cables. Cap nuts are also used where the view of screw and nut would be annoying, for example with furniture.

Collar nut

A collar nut is a normal or high hexagon nut that is enlarged on one of the two end faces with a washer - similar to a washer . This distributes the screwing force over a larger area, which is an advantage with soft counter-materials such as aluminum and plastics. The contact surface on the collar nut can also be provided with locking teeth, which leads to a form fit with the soft counterpart.

  • Standard: DIN 6331

Shared mother

A split nut can be attached to a threaded bolt from the sides. An ordinary nut, axially separated into two or more parts, is put together around the circumference of the screw, and its parts are connected together.

With the “split nut” from the brand TwinNut, two externally identical nut halves, which differ by only half a thread pitch, are pushed together from two sides. Their mutual radial connection is positive after the nut is tightened. Additional fasteners - as with older split nuts - are not required.

Nuts for connection with metal sheets

Sheet metal is usually too thin to cut a load-bearing thread into it. They are usually connected permanently with special nuts, for example in body construction . Only a few of the large number of available solutions are described below.

Weld nut

Weld nuts (see illustration ) are connected to the sheet metal by resistance welding (projection welding). For this purpose, the nut has a centering shoulder and several pointed welding lugs on the welding side.

It is not necessary to hold the nut back when tightening the screw. Weld nuts are therefore used in hard-to-reach places in body and housing construction.

A welding nut is difficult to weld onto pre-treated components (painted or similar). Corrosion protection treatment must often be applied after welding.

Set nut or press-in nut

Setting nuts usually have a toothed collar that is pressed into a hole in the sheet metal. The screw is screwed in from the rear. The toothing of the collar, which is buried in the sheet metal, absorbs the tightening torque.

Blind rivet nuts are also known as setting nuts (see illustration ). These are an alternative to weld nuts if the rear of the installation site is generally not accessible (fence posts, pipes, containers). See also blind rivet . They can also be used in pre-lacquered or galvanized sheet metal and without post-treatment for corrosion protection.

Cage nut

Cage nut

A cage nut has a cage-like structure by means of which it can be snapped into a hole in a sheet metal and thus fixed to the sheet metal.

The illustration opposite shows a cage nut that belongs to a special assembly system . It can be mounted in the U-profile rod from the side and snaps into the square hole in the profile side.

Snap nut

A snap nut, also known as a body or sheet metal nut, is a nut that is carried by a U-shaped resilient sheet metal bracket. The counter leg of the bracket contains a through hole. It can be pushed over the edge of a sheet metal with which it is positively connected when the screw (sheet metal or machine screw) is screwed in together with the part to be fastened. The sheet is drilled through beforehand at the relevant point.

Nuts for screwing furniture

Sleeve nuts with matching screws
Cross threaded bolt QD / M6-7.5 / 13x16.2

Only a few of the large number of available solutions are described below.

Sleeve nut

A sleeve nut is a thin hollow cylinder with an internal thread and a screw head. It is inserted into a through hole and locked from the opposite side with a suitable screw. This means that the connection has a screw head on both sides. Sleeve nuts with a flat head are used as book screws .

Cross nut bolt

A cross nut bolt (wrongly also cross-threaded bolt) is a bolt with a threaded hole made transversely to the bolt axis. With its help, a plate can be screwed to another plate at right angles. It is inserted into a hole that is drilled in the normal direction in one of the two plates. The screw hole is drilled from one edge up to the bolt hole. The screw runs through the other plate in the normal direction. A slot in one end of the bolt is used to align the cross hole.

There is no manufacturer-independent uniform designation scheme. The following are usually named: bolt diameter and length, thread and thread position (distance from one end).

Drive-in nut

Drive-in nut

One possible form of a drive-in nut has a cylindrical shape - fitting into a pre-drilled hole - and a toothed washer (similar to a specific pushpin ). The teeth of this disk are knocked into the board, they support the torque. Another common shape is weakly toothed on the outer cylinder. Here, too, there is a form fit against twisting after hammering. The advantage of this nut shape is its quick assembly, which is why it is often used for blind constructions in trade fair and exhibition construction as well as blind or substructures in furniture construction. It is flush with the component surface, which means that it does not have to be embedded like a conventional hexagon nut, which is more complex and, on top of that, weakening the bore.

Screw-in nut / threaded socket / ramp socket

Screw-in nut / threaded socket

A screw-in nut is a hollow cylinder with a metric internal thread and opposing (mostly coarse) wooden external threads. It is particularly widespread in furniture construction.

The advantage of the screw-in nut / threaded sleeve over the drive-in nut is that (if access is difficult via the outside of the component) assembly can be carried out from the same side from which the machine screw is then screwed in. It therefore also does not necessarily require a through-hole that is visible in the surface of the component outside and is therefore mostly undesirable. Another advantage of this nut is that the screw-in depth can be selected and varied continuously within the limits, which i. d. R. means that for aesthetic reasons it can be set flush with the surface of the component.

When screwing into a pre-drilled blind hole or through hole corresponding to the core diameter of the sleeve , the coarse external wood screw thread cuts into the wood or wood-based material wall and acts there both positively and non-positively. For screwing in, the screw-in nut in its standard form has a slot at one end that allows it to be turned with a wide screwdriver ; alternatively, there are designs for hexagon socket tools (INBUS), e.g. B. at IKEA. A metric screw can then be screwed in.

The screw-in nut is standardized under DIN 7965. The term "ramp socket" is often used synonymously , although the name RAMPA is a protected brand name of the company Hans Brügmann GmbH & Co. screw factory from Büchen . The Rampamuffe was invented in 1905 by Hermann Brügmann. They come in many different varieties these days. Special designs are intended for screwing into stone, metal, mineral materials and plastics, e.g. B. also in motorcycle cylinder housings, when the originally cut metric thread is torn out. The thread insert offers a similar solution for this .

Nuts connected to other components

A mother's connection with another part is often referred to as a mother, although the new unit contains another part and a new function.

Ring nut

The ring nut is a nut connected to a ring. The ring is arranged upright on one of the two end faces of the nut. The purpose of an eye bolt is to connect a ring (or an eyelet) to a threaded rod. A rope or a hook is often passed through the eye, for example when used as a so-called crane eye .

Turnbuckle nut

Turnbuckle : hook
screw with right-hand thread (left); Eye bolt with left-hand thread (right)

A turnbuckle nut is part of a turnbuckle , the other parts of which are two threaded hooks or eyelets, each with a right-hand and left-hand thread. The turnbuckle nut is made up of a right-hand and left-hand threaded nut. They are connected to each other at a certain distance on the same axis. The connection is made with a cylindrical housing or simply with two short rods (see illustration). By turning the turnbuckle nut, the two threaded rods are drawn together or removed from each other depending on the direction of rotation. Turnbuckles are often used to tension wires, e.g. B. used in garden fences and on pastures.

  • Standard: DIN 1479

T-slot nut

A T-nut nut only has a threaded hole in a T-nut block (also known as a "slot nut"). Such a stone is used to connect the machine table and the workpiece in a machine tool . It can be moved axially in a T-slot on the table. With it, a screwing point is created for the workpiece by means of a corresponding special screw.

Spindle nut

A spindle nut , sometimes also called a movement nut , is a component of a screw drive and therefore not a fastening element, but part of a linear drive .

See also

Individual evidence

  1. H. Ott: Maschinenkonstruktion , Volume IIIa, AMIV-Verlag Zürich 1978, page 41.
  2. Federal Aircraft Accident Investigation Bureau: Report 11 3X046 - Accident on May 8, 2011 , Braunschweig, March 16, 2012, accessed on October 20, 2013.
  3. All-steel lock nut: Product description ( archived copy ( memento of the original dated December 30, 2013 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. ). @1@ 2Template: Webachiv / IABot /
  4. DIN 546
  5. TwinNut: Product description ( PDF  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. ).@1@ 2Template: Dead Link /  
  6. ↑ Pushing together is pivoting on a circular path with a slight curvature. When the nut is tightened against an annular surface, pivoting is prevented with a positive fit. [1] .
  7. ↑ Nut made of two parts connected with pins ( PDF  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. ).@1@ 2Template: Toter Link /  
  8. Set nuts at Auel Connection Technology GmbH ( Memento of the original from March 27, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 264 kB) @1@ 2Template: Webachiv / IABot /
  9. Snap nuts at Auel Connection Technology GmbH ( Memento of the original from July 14, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 482 kB). @1@ 2Template: Webachiv / IABot /
  10. Sleeve nut from Schrauben-Jäger (PDF; 76 kB).

Web links

Commons : Nuts  - collection of images, videos and audio files
Wiktionary: Mother  - explanations of meanings, word origins, synonyms, translations