The Manual of Fastening 5 edition Technology
Dealing with the complex field of fastening technology every day means there are always questions to answer that go beyond the information normally provided in the standards. The aim of this manual is to provide an overview of the technology associated with threaded fasteners, in order to help users in answering these questions. The information provided brings together details of the relationships between products and their mechanical properties, gives advice for arranging, securing and fitting fasteners, explains why
these factors are significant, and outlines important aspects for everyday use. The first edition of ??The Manual of Fastening Technology?? was published in 1987. The content of the third edition published in 2002, which this edition supersedes, has been comprehensively revised and updated. Our Application Engineering team is always standing by to offer expert advice should you require any further support.
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Selection and analysis Standards Materials Manufacture Threads Assembly Self-tapping fasteners Fastener retention Corrosion protection ECOTECH
10 ?C 15 16 ?C 25 26 ?C 43 44 ?C 51 52 ?C 60 61 ?C 66 67 ?C 74 75 ?C 83 84 ?C 100 101 ?C 102
Section 1 Section 2 Section 3 Section 4 Section 5 Section 6 Section 7 Section 8 Section 9 Section 10
Selection and analysis
The threaded fastener is one of the most universal and widely used types of fastener and is manufactured in a wide variety of shapes and sizes. Many types of design are standardised internationally and available throughout the world.
due to the forces acting on the connection. Conversely, the preload force selected must not be so high as to cause the permissible stresses in the joined components to be exceeded during service. The proper design of a threaded connection for a given set of components is not only dependent on positioning and the selection of an appropriate assembly method, but also, most importantly, on the quality of the design of
the fastener itself. A large number of different sizes, standards, materials and property classes are available. It remains the task of the user to make the correct choice to provide the preload force required in each case.
The classic threaded connection is formed by joining two or more components by means of form-fit or friction-fit fasteners. The tightening torque applied to the threaded fastener generates a preload force that clamps the components together, thereby creating a frictional connection between all the contacting surfaces. With a properly designed threaded connection, the preload force is high enough to prevent any relative movement between the components
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Designing a threaded connection
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Selection and analysis
Threaded connections should be designed in such a way that the permissible stresses in the mating components are never exceeded by the forces acting on the connection as a whole. The tightening torque should be selected such that the preload force produced creates a purely frictional connection between the components and thus prevents them from sliding against each other or having to be supported by the shaft of the fastener (as compared to a rivet connection). Guideline value: Preload force should be at least equal to 75% of the yield stress in the fastener. A detailed procedure for the analysis and design of threaded connections can be found in VDI Guideline 2230. All forces that occur give rise to deformation and the possibility of displacement of the joined components. As long as the sum of all forces does not cause failure of one of the components or fasteners, the assembly acts as a unit. However, where dynamic loads are present ?C particularly
vibration ?C it is possible for effects to occur that cause the threaded connection to work loose, although the permissible values are not exceeded, e.g. due to components moving relative to each other along the axis of the fastener. This effect is referred to as self-loosening. Applying a tightening torque indirectly causes a preload force to act on the fastener, which in turn leads to elongation of the fastener and contraction of the joined components. Forces that occur in use are distributed according to the elasticity of the mated parts. Under tensile stress, the load on the fastener is only reduced slightly, whereas the remaining clamping force decreases significantly.
Threaded fastener Tightening torque
Selection and analysis
The elastic elongation of the fastener that occurs as a result of the preload force means that the frictional connection between the components remains intact under additional loading, particularly impact loading.
require additional retention measures, provided that no increased dynamic loads are likely, especially perpendicular to the axis of the fastener. In other cases, the use of additional means of fastener retention should be considered. Important: Any compressible spring elements used in conjunction with the fastener will affect the load ratios.
With a clamping length ratio of Lk / DNom > 5, a low number of contact surfaces and sufficient preload force, metallic components do not
Sum of forces acting on the fastener Preload force Force occurring in service Preload force
Contraction of the preloaded components Change in length
Elongation of the fastener
Selection and analysis
Effects of friction During fitting of the threaded fastener, the preload force can only be regulated indirectly via the tightening torque that is applied, which means that a precise knowledge of the friction
characteristics is of decisive importance. It is necessary to distinguish between the friction in the thread itself and that at the bearing surfaces.
Normal force FG
Friction angle ?Ì
Friction force FR
The friction angle, ?Ì, describes the ratio of the normal force, FG, to the friction force, FR, which it generates. Taken in the context of a threaded connection, normal force and preload force can be considered equal as a first approximation. Provided that the pitch angle, ?, of the thread is greater than the friction angle, ?Ì, the thread will be self-locking. In order to enhance this effect, it
is therefore possible to either increase the thread friction or to reduce the thread pitch. The effect of friction at the bearing surfaces is considerably more difficult to determine. It is nonetheless possible to establish that, for a given tightening torque, an increase in friction, e.g. below the head of the fastener, on the one hand reduces the preload force, but on the other hand counteracts self-loosening of the fastener.
Selection and analysis
Design The selection of the required fastener diameter and property class relies upon a precise knowledge of all loads that might occur, and is thus dependent on the specific application. It is necessary here to distinguish between connections formed using a clearance hole (bolts) and internally threaded holes (screws). When designing through-bolted connections, the nominal length of the bolt is given by the sum of the clamping length (lk) and the bolt end protrusion (v) (as in DIN 78 Bolt end protrusions). Compliance with the specified bolt end protrusions is of particular importance for a secure connection.
There are, however, a few generally applicable guidelines that can be followed with regard to the length of the fastener. The most important factor is that sufficient load-bearing turns of the thread are engaged to be able to withstand all forces that may occur.
lk: clamping length v: bolt end protrusion l: nominal length of the bolt Hexagon head bolt with hexagon nut Hexagon head bolt with lock nut Choosing an appropriate nut is very straightforward provided the property class of the bolt is known (a bolt of property class 8.8 must be paired with a nut of property class 8 or higher). By contrast, the required length of engagement (le) for an internally threaded connection is a function of the material strength of the part into which the internal thread is tapped.
le: length of engagement d: screw diameter lg: useful thread
Selection and analysis
Material of components 3.6 / 4.6 Steel with Rm N/mm2 ?Ü 400 400????600 > 600????800 > 800 0.8 ?? d 0.8 ?? d 0.8 ?? d 0.8 ?? d 1.3 ?? d 1.3 ?? d Cast Al alloys Pure aluminium Al alloy, hardened not hardened 1.6 ?? d 1.6 ?? d 0.8 ?? d 1.2 ?? d 2.5 ?? d
Length of engagement le2) according to property class of screw 4.8????6.8 1.2 ?? d 1.2 ?? d 1.2 ?? d 1.2 ?? d 1.5 ?? d 1.3 ?? d 2.2 ?? d ?C 1.2 ?? d 1.6 ?? d ?C 8.8 ?C 1.2 ?? d 1.2 ?? d 1.0 ?? d 1.5 ?? d ?C ?C ?C 1.6 ?? d ?C ?C 10.9 ?C ?C 1.2 ?? d 1.0 ?? d ?C ?C ?C 3) ?C 3) ?C 3) ?C 3) ?C
Cast iron Copper alloys Light metals1)
Soft metals, plastics
1) 2) 3)
For dynamic loads the specified value of le must be increased by approx. 20%. Source: Roloff / Matek Fine pitch threads require approx 25% greater lengths of engagement. For higher strength screws, the shear strength of the internal thread material as calculated in VDI 2230 must be taken into account.
When determining the nominal length of threaded fasteners, the tolerances applicable to the parts to be joined must be considered. In addition to this, the tolerances on the screw or bolt length and nut height must be taken into account.
The calculated length must ?C whenever possible ?C be rounded to the next highest nominal length, as specified in the appropriate product standard (dimensional standards).
By way of departure from the above specifications, a smaller length of engagement is permitted when using a HELICOIL? thread insert. See DIN 8140. Example: M 8 screw of property class 10.9 mounted in aluminium with a tensile strength of Rm = 250 ???? 270 N/mm2 and a permissible shear stress of Tzul = 0.7 x Rm = 180 N/mm2 Without HELICOIL?: Thread length min 2 x d (as in VDI 2230) With HELICOIL?: Thread length 1.5 x d (as in DIN 8140?C1, 3.1).
Bolts, screws, studs, nuts, washers, pins, etc. are mechanical fasteners. The majority of these components is designated in accordance with standards, which specify shapes, types, dimensions, tolerances and mechanical properties.
The product standards also contain references to basic standards, which specify generally applicable basic requirements. These relate for example to threads, thread run-outs, thread ends, tolerances, force application, and acceptance testing. Product standard DIN EN ISO 4014
specifies the dimensions for hexagon head bolts. The letter symbols are explained in the table below.
DIN EN ISO 4014 / 8.8 M 12 x 50
The standard designation given above includes all relevant details of the component in question. Product standard DIN EN ISO 4014, which specifies the dimensions of hexgon head bolts, was preceded by DIN EN 24014. The above standard contains references to other standards dealing with materials, mechanical properties for individual property classes, and surface finish. Such standards are also known as functional standards.
Maximum underhead fillet
Point shall be chamfered or for threads ?Ü M 4 may be as-rolled (sheared end) (see ISO 4753)
Reference line for dw
From DIN EN ISO 4014
Key to dimensions b c d da ds dw e k k?? l lg ls r s Thread length Height of washer face Major diameter (nominal diameter) of thread Transition diameter Diameter of unthreaded shank Diameter of bearing surface Width across corners Height of head Wrenching height Nominal length Distance from last full form thread to bearing surface Length of unthreaded shank Radius of curvature under head Width across flats
These symbols and designations for dimensioning are specified in DIN EN 20225.
All other dimensions in the standard are derived from the nominal diameter and the length.
Thread d P M 12 1.75 l ?Ü 125 mm b Reference dimension l > 125 mm / l ?Ü 200 mm l > 200 mm ?C min. c max. da max. = Nominal dimension ds A min. Product grade B A dw min. Product grade B A e lf Nominal dimension min. A k Product grade min. B max. A kw r max. = Nominal dimension s min. Product grade B Extract from DIN EN ISO 4014 17.57 23.16 29.16 35 A min. Product grade B min. 5.05 0.6 18.00 17.73 6.8 0.6 24 23.67 8.51 0.8 30 29.67 10.26 0.8 36 35.38 7.79 5.12 10.29 6.87 12.85 8.6 15.35 10.35 7.21 9.71 12.15 14.65 max. 7.68 10.18 12.715 15.215 min. Product grade B max. 19.85 3 7.5 7.32 26.17 3 10 9.82 32.95 4 12.5 12.285 39.55 4 15 14.785 16.47 20.03 22 26.75 27.7 33.53 33.25 39.98 11.57 16.63 15.57 22.49 19.48 28.19 23.48 33.61 max. 0.6 13.7 12 11.73 0.8 17.7 16 15.73 0.8 22.4 20 19.67 0.8 26.4 24 23.67 30 36 49 0.15 M 16 2 38 44 57 0.2 M 20 2.5 46 52 65 0.2 M 24 3 54 60 73 0.2
Special design features To identify special design features in product designations, additional letter symbols are used. Example: ISO 4014/8.8 M 12 x 50 S means ??with split pin hole??.
Symbols for bolt/screw end features
Sym. A Ak B C C CH CN CP F FL Fo H L LD LH N PC PF R Ri RL Bolt/screw end feature Threaded up to the head (DIN 962) Rounded short dog point (DIN 962) Shank diameter ?Ö pitch diameter (DIN 962) Shank diameter ?Ö thread diameter (DIN 962) Tapping screw with cone point (DIN EN ISO 1478) Chamfered end (DIN EN ISO 4753) Cone point (DIN EN ISO 4753) Cup point (DIN EN ISO 4753) Tapping screw with full dog point (DIN EN ISO 1478) Flat point (DIN EN ISO 4753) Studs without interference fit thread (DIN 962) Philips - cross recess Washers for screw and washer assemblies (large) (DIN EN ISO 10644) Long dog point (DIN EN ISO 4753) Left-hand thread (DIN 962) Washers for screw and washer assemblies (medium) (DIN EN ISO 10644) Pilot point with truncated cone (DIN EN ISO 4753) Pilot point, flat (DIN EN ISO 4753) Tapping screws with rounded end (DIN EN ISO 1478) Thread undercut (DIN 76-1) As-rolled end (DIN EN ISO 4753) Example A M 6 x 40 M 10 x 50 Ak B M 8 x 80 C M 12 x 90 ST 3.5 x 9.5 C M 10 x 50 CH M 10 x 50 CN M 10 x 50 CP ST 3.5 x 9.5 F M 10 x 50 FL M 10 Fo x 50 M 5 x 20 H M 10 x 50 S2-L M 10 x 50 LD M 12 LH x 75 M 10 x 50 S2-N M 10 x 50 PC M 10 x 50 PF ST 3.5 x 9.5 R M 10 x 50 Ri M 10 x 50 RL Figure
Symbols for bolt/screw end features (continued)
Sym. RN S S S1-S6 Bolt/screw end feature Rounded end (DIN EN ISO 4753) Split pin hole (DIN 962/DIN 34803) Washers for screw and washer assemblies (small) (DIN EN ISO 10644) Various types of head for screw and washer assemblies with plain washers S, N or L (DIN EN ISO 10644) Scrape point (DIN EN ISO 4753) Short dog point (DIN EN ISO 4753) Securing hole in head/wire hole (DIN 962/DIN 34803) Slot Truncated cone point (DIN EN ISO 4753) Pozidriv ?C cross recess Screw and washer assembly with type S (small series) plain washer (DIN EN ISO 10644) Screw and washer assembly with type N (normal series) plain washer (DIN EN ISO 10644) Screw and washer assembly with type L (large series) plain washer (DIN EN ISO 10644) Example M 10 x 50 RN M 10 x 50 S M 10 x 50 S2-S M 10 x 50 S2-N Figure
SC SD Sk
M 10 x 50 SC M 10 x 50 SD M 10 x 50 Sk M 10 x 50 Sz M 10 x 50 TC
M 5 x 20 Z M 10 x 50 Z 0 M 10 x 50 Z 1 M 10 x 50 Z 2
Sz TC Z Z0 Z1 Z2
Correlation of old and new symbols for bolt/screw end features With the publication of DIN EN ISO 4753, which has to a large extent replaced DIN 78, a number of symbols designating bolt/screw end features (previously referred to as ??thread ends??) have been amended. For ease of reference, the table below correlates the old symbols with those used in DIN EN ISO 4753.
Old symbol K Ka Ko Ks L Rs Sb Sp Za Bolt/screw end feature Chamfered end Short dog point As-rolled end Flat point Rounded end Cup point Scrape point Truncated cone point Long dog point New symbol CH SD RL FL RN CP SC TC LD
Standards are technical rules These technical rules can be referred to by everybody. The standards that are valid in Germany are published and updated by DIN, the German Institute for Standardization. The Institute is based in Berlin and administers approximately 29,500 DIN Standards, of which over 386 are applicable to mechanical fasteners. The DIN German Institute for Standardization has around 1,745 members, drawn from trade and industry, the sciences and the service sector. Over 26,278 experts are active on behalf of DIN. Standards are developed by working groups. The drafts of a standard are made available to all interested parties and following a consultation period, published as official standards. In order to simplify international exchange of goods and avoid barriers to trade, national standards are being superseded by international standards. This means that consistent terminology and definitions are available internationally, that quality standards are unified at a high level, and that products can be exchanged throughout the world. The ISO, the "International Organization for Standardization", is headquartered in Geneva and is responsible for international standardisation. More than 157 countries are members of this organisation. Its output is published under the name ISO.
Many ISO Standards are adopted as European Standards and by this means attain the status of a DIN Standard (DIN EN ISO). Other ISO Standards are adopted directly as DIN Standards (DIN ISO). The 29 members of CEN (European Committee for Standardisation) are obliged to adopt European Standards as part of their respective national bodies of standards. Conflicting national standards must be withdrawn. This means that there are various designations for standards. DIN ISO DIN ISO EN DIN EN EN ISO German national Standard International Standard German version of an unchanged ISO Standard European Standard German version
of a European Standard European version of an unchanged ISO Standard
DIN EN ISO German version of an EN ISO Standard Product markings use simply DIN or ISO. The products covered by DIN EN ISO 4014 are identified as ISO 4014 in drawings, parts lists, commercial documents and on packaging.
Conversion from DIN to ISO Changes that affect the various product groups as a result of the conversion are listed below: Changes in standards applying to hexagon head products
DIN 931 601 933 558 960 961 934 439 ISO 4014 4016 4017 4018 8765 8676 4032 4035 8673 10642 Description Hexagon head bolts (Product grades A and B) Hexagon head bolts (Product grade C) Hexagon head screws (Product grades A and B) Hexagon head screws (Product grade C) Hexagon head bolts with metric fine pitch thread (Product grades A and B) Hexagon head screws with metric fine pitch thread (Product grades A and B) Hexagon nuts, style 1 (Product grades A and B) Hexagon thin nuts (chamfered) (Product grades A and B) Hexagon nuts, style 1, with metric fine pitch thread (Product grades A and B) Hexagon socket countersunk head screws
Changes in widths across flats
Thread diameter Small hexagon DIN 561, 564 DIN M 10 M 12 M 14 M 16 M 20 M 22 ?C 17 ?C 19 ?C ?C ISO ?C 16 ?C 18 ?C ?C Standard hexagon Large hexagon HV products DIN ?C 22 ?C ?C 32 ?C ISO ?C 21 ?C ?C 34 ?C Square DIN 478, 479, 480 DIN ?C ?C ?C 17 22 ?C ISO ?C ?C ?C 16 21 ?C
DIN 17 19 22 ?C ?C 32
ISO 16 18 21 ?C ?C 34
Changes to heights of hexagon nuts
Thread d DIN 934 min. M5 M6 M7 M8 M 10 M 12 M 14 M 16 M 18 M 20 M 22 M 24 M 27 M 30 M 33 M 36 M 39 3.7 4.7 5.2 6.14 7.64 9.64 10.3 12.3 14.3 14.9 16.9 17.7 20.7 22.7 24.7 27.4 29.4 max. 4 5 5.5 6.5 8 10 11 13 15 16 18 19 22 24 26 29 31 m/d **) 0.8 0.83 0.79 0.81 0.8 0.83 0.79 0.81 0.83 0.8 0.82 0.79 0.81 0.8 0.79 0.81 0.79 min. 4.4 4.9 6.14 6.44 8.04 10.37 12.1 14.1 15.1 16.9 18.1 20.2 22.5 24.3 27.4 29.4 31.8 Nut height m ISO 4032 Type 1 max. 4.7 5.2 6.5 6.8 8.4 10.8 12.8 14.8 15.8 18 19.4 21.5 23.8 25.6 28.7 31 33.4 m/d **) 0.94 0.87 0.93 0.85 0.84 0.90 0.91 0.92 0.88 0.90 0.88 0.90 0.88 0.85 0.87 0.86 0.86
**) Note: m/d is the ratio of nut height to thread diameter