BSI Standards PublicationHigh-strength structural bolting assemblies for preloading Part 3: System HR — Hexagon bolt and nut assemblies... NORME EUROPÉENNE English Version High-strength
Dimensions of bolts
The difference between l g and l s should not be less than 1,5 P
For coated bolts, the dimensions apply prior to coating
The data presents various parameters with specific maximum and minimum values across different categories For instance, the parameter "P" ranges from 1.75 to 2.5, while "c" values are listed as 30, 34, 38, 42, and 46 The maximum and minimum values for "da" are 15.2 to 24.4, and for "ds," they range from 11.30 to 20.84 The minimum values for "dw" start at 20.1 and go up to 29.5, while "e" ranges from 23.91 to 35.03 The nominal values for "k" are between 7.5 and 12.5, with maximums reaching 13.40 and minimums at 7.05 Additionally, "kw" has minimum values from 4.90 to 8.10, and "r" is consistently at 1.2 or 1.5 Lastly, the parameters "s" and "l" show a range of minimum and maximum values, indicating a structured dataset for analysis.
The data presents various parameters with specific values across different categories For instance, the reference values for P range from 2.5 to 4, while the maximum and minimum values for c are 78 and 50, respectively The maximum values for d are noted as 84, with a minimum of 56 In terms of e, the values range from a minimum of 69 to a maximum of 97 The maximum and minimum values for da are 42.4 and 26.4, respectively, while ds shows a maximum of 37.00 and a minimum of 21.16 The minimum values for dw are between 33.3 and 55.9, and for e, they range from 39.55 to 66.44 The nominal values for k are listed from 14 to 22.5, with maximum values reaching 23.55 and minimum values at 13.10 The kw values start at a minimum of 9.2, and the r values are consistently at a minimum of 1.5 Lastly, the s values range from a minimum of 35.0 to a maximum of 60, indicating a structured dataset with defined limits across various parameters.
Preferred lengths are categorized as ls,min and lg,max, with non-preferred sizes indicated The pitch of the thread is denoted as P For nominal lengths, specific ranges are defined: lengths lnom ≤ 125 mm, 125 mm < lnom ≤ 200 mm, and lnom > 200 mm The maximum diameter is given by d w,max = s actual, while lg,max is calculated as lnom – b ls,min = lg,max – 5P If ls,min, as determined by the formula, is less than 0.5d, the bolts must be fully threaded, making lg,max equal to amax as specified in ISO 3508 for product grade C, which is 4P Fully threaded bolts are represented above the stepped line.
Specification for bolts and reference standard
Table 3 — Specifications for bolts and reference standards
General requirements EN 14399-1 and EN 14399-2
Mechanical properties Property class 8.8 or 10.9
Tolerances Product grade C except for dimensions c and r
Tolerance for lengths ≥ 160 mm: ± 4,0 mm
Hot dip galvanized EN ISO 10684
Surface integrity Limits for surface discontinuities as specified in
For the acceptance procedure, refer to EN ISO 3269 The specified tolerance class applies to bolts prior to any coating, with hot-dip galvanized bolts designed for use with nuts that are tapped oversize to 6AZ It is crucial to consider the risk of hydrogen embrittlement for bolts of property class 10.9 when selecting surface treatment processes, as outlined in the relevant coating standards "As processed" refers to the standard finish from manufacturing, which includes a light oil coating Alternative coatings may be negotiated between the purchaser and manufacturer, provided they do not compromise mechanical properties or functional characteristics; however, coatings of cadmium or cadmium alloy are prohibited.
Marking of bolts
High-strength structural bolts according to this part of this document shall be marked with: a) property class marking in accordance with EN ISO 898-1 and the letters HR;
EXAMPLE 10.9 HR b) the identification mark of the manufacturer of the bolting assembly
It is permissible for the marking to be either embossed or indented on the top surface of the head For bolt marking, see Figure 2:
1 identification mark of the manufacturer of the bolting assembly
Figure 2 — Example of bolt marking
Dimensions of nuts
For coated nuts the above dimensions apply prior to coating
P b 1,75 2 2 2,5 2,5 2,5 3 3 3,5 4 da max 13,0 15,1 17,3 19,5 21,6 23,7 25,9 29,1 32,4 38,9 min 12 14 16 18 20 22 24 27 30 36 dw max c c c c c c c c c c min 20,10 21,86 24,90 27,70 29,50 33,30 38,00 42,80 46,60 55,90 e min 23,91 27,12 29,56 32,95 35,03 39,55 45,20 50,85 55,37 66,44 m max 10,8 12,8 14,8 15,8 18,0 19,4 21,5 23,8 25,6 31,0 min 10,37 12,10 14,10 15,10 16,90 18,10 20,20 22,50 24,30 29,40 mw min 8,3 9,7 11,3 12,1 13,5 14,5 16,2 18,1 19,5 22,4 c max 0,8 0,8 0,8 0,8 0,8 0,8 0,8 0,8 0,8 0,8 min 0,4 0,4 0,4 0,4 0,4 0,4 0,4 0,4 0,4 0,4 s max 22 24 27 30 32 36 41 46 50 60 min 21,16 23,16 26,16 29,16 31,00 35,00 40,00 45,00 49,00 58,80 t 0,38 0,42 0,47 0,52 0,58 0,63 0,72 0,80 0,87 1,05 a Non-preferred sizes b P is the pitch of thread c d w,max = s actual
Specification for nuts and reference standards
Table 5 — Specifications for nuts and reference standards
General requirements EN 14399-1 and EN 14399-2
Coating of the bolt Uncoated Hot dip galvanized Others Tolerance class of the nut 6H 6AZ 6H a
Mechanical properties Property class 8 b or 10 b
Tolerances Product grade B except for dimensions m and c
Hot dip galvanized EN ISO 10684
Surface integrity Limits for surface discontinuities as specified in
For the acceptance procedure, refer to EN ISO 3269 Oversize tapped nuts with a thread tolerance class up to 6AZ may be utilized for coatings requiring increased fundamental deviation, as per the relevant standard For mechanical properties beyond those outlined in EN ISO 898-2, consult Table 6 for proof load values and Table 7 for hardness values Tolerances on perpendicularity of the bearing face are specified in Table 4 The term "as processed" refers to the standard finish achieved during manufacturing, which includes a light oil coating Alternative coatings can be discussed between the purchaser and manufacturer, provided they do not compromise mechanical properties or functional characteristics; however, coatings of cadmium or cadmium alloys are prohibited.
Proof load values of nuts
Table 6 — Proof load values of nuts
Nominal stress area of standard test mandrel
Tolerance class 6H to 6AZ Tolerance class
6H to 6AZ mm 2 Proof load (A s × S p), N
NOTE The proof load values are based on the following stress under proof load (S p):
— for nuts of property class 8: 1 000 N/mm 2
— for nuts of property class 10: 1 160 N/mm 2
Where nuts are to be accepted on the basis of hardness values, the appropriate limits are those specified in Table 7
Table 7 — Hardness values of nuts, if specified
According to EN ISO 898-2, property class 8 features a tolerance class of 6H, while property class 10 can have a tolerance class of either 6H or 6AZ Additionally, property class 8 with a tolerance class of 6AZ is hot dip galvanized, exhibiting hardness levels ranging from 260 HV to 353 HV, equivalent to 24 HRC to 36 HRC.
Decarburization of the nut thread
The decarburization of the nut thread, when measured in analogy to external threads, as given in
EN ISO 898-1, shall not exceed G = 0,015 mm.
Marking of nuts
High-strength structural nuts according to this document shall be marked with: a) property class marking in accordance with EN ISO 898-2 and the letters HR;
EXAMPLE 10 HR b) the identification mark of the manufacturer of the bolting assembly
Marking on chamfered nuts must be indented on either bearing face, while washer faced nuts can have markings that are either indented or embossed on the non-bearing face For visual reference, please refer to Figure 4.
1 identification mark of the manufacturer of the bolting assembly
Figure 4 — Example of nut marking
5 Designation of the bolt/nut assemblies
The designation of bolt/nut assemblies is specified in this clause The complete designation for bolting assemblies includes washers specified in EN 14399-6 and/or EN 14399-5
The article discusses the designation of a high-strength structural bolting assembly for preloading, specifically system HR It includes a hexagon head bolt with a large width across flats, featuring an M16 thread, a nominal length of 80 mm, and a property class of 8.8 Additionally, it describes a hexagon nut with a large width across flats, also with an M16 thread and a property class of 10, finished as processed according to k-class K0 This assembly is suitable for use with a direct tension indicator in compliance with EN 14399-9.
Bolt/nut assembly EN 14399-3 — HR — M16 × 80 — 8.8/10 — K0
The article discusses the designation of a high-strength structural bolting assembly, specifically a hexagon head bolt and nut system designed for preloading The bolt features a large width across flats, an M16 thread, a nominal length of 80 mm, and a property class of 10.9 The accompanying hexagon nut also has a large width across flats, an M16 thread, and a property class of 10 Additionally, both components are coated with hot-dip galvanized zinc, adhering to k-class K2 standards.
Bolt/nut assembly EN 14399-3 — HR — M16 × 80 — 10.9/10 — tZn — K2
Bolt/nut assemblies according to this document shall be assembled with washers specified in EN 14399-6 and/or EN 14399-5 (under the nut only)
7 Functional characteristics of the bolt/nut/washer(s) assembly
General
The functional characteristics of the bolt/nut/washer(s) assemblies according to 7.2 and 7.4 shall be achieved for all k-classes when tested in accordance with EN 14399-2
Additionally for K1, 7.5.1 shall apply and for K2, 7.5.2 shall apply
Minimum clamp lengths are specified in Annex A (see Table A.1)
NOTE For further background information as to these functional characteristics, see EN 14399-2
To prevent seizure during the tightening process and achieve the necessary preload, the bolting assembly must be adequately lubricated in its delivered state.
Maximum individual value of the bolt force during fitness for purpose test (F bi,max)
The following applies: s ub max
F ≥ × where f ub is the nominal tensile strength (R m);
A s is the nominal stress area of the bolt.
Values of angle Δθ 1
Δθ 1 is the angle by which the nut shall be turned starting from a preload of 0,7 f ub × A s until F bi,max is reached The values indicated in Table 8 are for information only
6 d ≤ Σt ≤ 10 d 150° a Σt is the total thickness of the clamped parts including washer(s).
Values of angle Δθ 2
Δθ 2 is the angle by which the nut shall be turned, starting from a preload of 0,7 f ub × A s through F bi,max and until
F bi has dropped to 0,7 f ub × A s
The values for Δθ 2 specified in Table 9 apply
6 d ≤ Σt ≤ 10 d 270° a Σt is the total thickness of the clamped parts including washer(s).
Individual values of the k-factor (k i ), mean value of the k-factor (k m ) and coefficient of
Individual values of the k-factor (k i ) for k-class K1
For k-class K1, the k i values shall be within the range of 0,10 ≤ k i ≤ 0,16.
Mean value of the k-factor (k m ) and coefficient of variation of the k-factor (V k ) for k-
The mean value (k m) of the k-factor shall be calculated as follows: n k k n
M pi is the individual value of the applied torque;
F p,C is the required preload; d is the nominal bolt diameter
The coefficient of variation of the k-factor (V k) shall be calculated as follows: m k k k
V = s where s k is the standard deviation
For k m and V k the following values apply:
Clamp lengths and grip lengths
Clamp lengths for bolting assemblies with one or two washers
See Figure A.1 and Table A.1 a) Clamp length with one washer b) Clamp length with two washers
NOTE 1 Clamp length is not affected by the number of washers
NOTE 2 The number of washers is dependent on the specific application as specified in EN 1090-2
Table A.1 — Clamp Length with one or two washers Σ t
Thread (d) M12 (M14) M16 (M18) M20 M22 M24 M27 M30 M36 l Σt min and Σt max nom min max min max min max min max min max min max min max min max min max min max min max.
Thread (d) M12 (M14) M16 (M18) M20 M22 M24 M27 M30 M36 l Σt min and Σt max nom min max min max min max min max min max min max min max min max min max min max min max.
The clamp lengths, denoted as Σt, are calculated using specific formulas for bolting assemblies with one or two washers The maximum clamp length is given by the equation Σt max = l min − m max − 1P For fully threaded bolts, the minimum clamp length is calculated as Σt min = a max + 4P, while for partially threaded bolts, it is Σt min = l g,max + 4P Here, Σt represents the total thickness of the clamped parts between the nut bearing face and the bolt bearing face, measured in millimeters, with m indicating the height of the nut and l representing the length of the bolt.
The P thread pitch is measured in millimeters (mm) and refers to the distance from the bolt bearing face to the first full profile thread Additionally, the lg distance, also measured in millimeters, indicates the distance from the bolt bearing face to the first full form thread.
Grip lengths for bolting assemblies with one or two washers
Bolting assemblies with one washer, see Figure A.2 and Table A.2
Figure A.2 — Grip Length with one washer t s1
Table A.2 — Grip lengths with one washer t s1
Thread (d) M12 (M14) M16 (M18) M20 M22 M24 M27 M30 M36 l t s1,min and t s1,max nom min max min max min max min max min max min max min max min max min max min max min max.
Thread (d) M12 (M14) M16 (M18) M20 M22 M24 M27 M30 M36 l t s1,min and t s1,max nom min max min max min max min max min max min max min max min max min max min max min max.
The grip lengths \( t_{s1} \) are calculated using the following formulas: \[t_{s1,\text{max}} = l_{\text{min}} - m_{\text{max}} - h_{\text{max}} - 1P\]\[t_{s1,\text{min}} = l_{g,\text{max}} + 4P - h_{\text{min}}\]Here, \( t_{s1} \) represents the total thickness of the clamped parts between the nut bearing face and the bolt bearing face, excluding the thickness of the washer, measured in millimeters (mm) The variables include \( l \) for the length of the bolt (mm), \( m \) for the height of the nut (mm), and \( h \) for the washer thickness (mm).
The P thread pitch is measured in millimeters (mm), while l g represents the distance from the bolt bearing face to the first full profile thread For fully threaded bolts, the maximum value of l g, denoted as l g,max, corresponds to the ‘a’max value for product grade C screws as specified in ISO 3508.
Bolting assemblies with two washers, see Figure A.3 and Table A.3
Figure A.3 — Grip Length with two washers t s2
Table A.3 — Grip lengths with two washers t s2
Thread (d) M12 (M14) M16 (M18) M20 M22 M24 M27 M30 M36 l t s2,min and t s2,max nom min max min max min max min max min max min max min max min max min max min max min max.
Thread (d) M12 (M14) M16 (M18) M20 M22 M24 M27 M30 M36 l t s2,min and t s2,max nom min max min max min max min max min max min max min max min max min max min max min max.
The grip lengths \( t_{s2} \) are calculated using the following formulas: \[t_{s2,\text{max}} = l_{\text{min}} - m_{\text{max}} - 2h_{\text{max}} - 1P\]\[t_{s2,\text{min}} = l_{g,\text{max}} + 4P - 2h_{\text{min}}\]Here, \( t_{s2} \) represents the total thickness of the clamped parts between the nut bearing face and the bolt bearing face, minus the thickness of the two washers, measured in millimeters (mm) The variables include \( l \) for the length of the bolt (mm), \( m \) for the height of the nut (mm), and \( h \) for the washer thickness (mm).
The thread pitch (P) is measured in millimeters (mm), while the distance (l g) from the bolt bearing face to the first full profile thread is also specified in mm For fully threaded bolts, the maximum distance (l g,max) corresponds to the ‘a’max value for product grade C screws as defined by ISO 3508.
[1] EN 1090-2, Execution of steel structures and aluminium structures - Part 2: Technical requirements for steel structures
[2] EN 1993-1-8, Eurocode 3: Design of steel structures - Part 1-8: Design of joints
[3] EN 14399-4, High-strength structural bolting assemblies for preloading - Part 4: System HV - Hexagon bolt and nut assemblies
[4] EN 14399-7, High-strength structural bolting assemblies for preloading - Part 7: System HR - Countersunk head bolt and nut assemblies
[5] EN 14399-8, High-strength structural bolting assemblies for preloading - Part 8: System HV - Hexagon fit bolt and nut assemblies
[6] EN 14399-9, High-strength structural bolting assemblies for preloading - Part 9: System HR or HV - Direct tension indicators for bolt and nut assemblies
[7] EN 14399-10, High-strength structural bolting assemblies for preloading - Part 10: System HRC - Bolt and nut assemblies with calibrated preload
[8] EN ISO 4032, Hexagon regular nuts (style 1) - Product grades A and B (ISO 4032)
[9] ISO 272, Fasteners - Hexagon products - Widths across flats
[10] ISO 888, Fasteners - Bolts, screws and studs - Nominal lengths and thread lengths