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  4. BS 3692 Specification

BS 3692 Bolts, BS 3692 Screws, BS 3692 Stud Bolts, BS 3692 Nuts

Recommended bolt and nut combinations

Grade of bolt 4.6 4.8 5.6 5.8 6.8 8.8 8.8 A) 10.9 10.9 A) 12.9
Recommended grade of nut 4 4 5 5 6 8 10 10 12 12
  • The nuts in Table 7 are at least 15% lower in height than ISO metric 'Regular' nuts, in BS EN ISO 4032 for example. Therefore they are not capable of withstanding the same tensile loads without the risk of thread stripping (see also Foreword)
  • Nuts of a higher strength grade may be substituted for nuts of a lower strength grade.

Chemical composition of steel nuts

Strength grade designation Chemical composition limit s (check analy si s)
C max. % Mn min. % P max. % S max. %
4, 5 and 6 (See notes) 0.5 0.11 0.15
8 0.58 0.3 0.06 0.15
10 and 12 (See notes) 0.58 0.45 0.048 0.058
  • Free cutting steel may be used only by special agreement between the purchaser and the supplier. In such cases, the following maximum phosphorus, sulfur and lead contents are permissible: Phosphorus, 0.12%; Sulfur, 0.34%; Lead, 0.35%.

EN 10269 Mechanical properties of steel nuts

Strength grade designation 4 5 6 8 10 12
Proof load stress A> MPa 400 500 600 800 1 000 1 200 - C)
Brinell hardness (HB) max. 302 302 302 302 353 375 All nuts
Rockwell hardness 8> (HRC) max. 30 30 30 30 36 39 All nuts
Vickers hardness (HV) max. 310 310 310 310 370 395 All nuts
  • A> The proof load is calculated by multiplying the proof load stress by the tensile stress area of the bolt .
  • B> The conversion from Brinell hardness into Rockwell hardness has been calculated in accordance with BS EN ISO 6506-1 BS EN ISO 6506-2 and BS EN ISO 6506-3, and BS EN ISO 6508-1.
  • C> All nuts other than those exempted by agreement between the purchaser and the manufacturer. Nuts with a specified proof load in excess of 500 000 N may be except from proof load test in g. Such nuts shall meet the minimum hardness as agreed between the purchaser and the manufacturer.

Proof loads for steel nuts (coarse pitch series)

Nominal size of ut m Tensile stress area of bolt mm2 Strength grade designat ion
4 5 6 8 10 12
Stress under proof load MPa
400 500 600 800 1000 1200
Proof load N
M1.6 1.27 510 640 760 1020 1270 1520
M2 2.07 830 1030 1240 1650 2070 2480
M 2.5 3.39 1360 1700 2030 2710 3390 4070
M3 5.03 2010 2520 3020 4000 5000 6000
M4 8.78 3510 4400 5250 7000 8750 10500
M5 14.2 5680 7100 8500 11400 14200 17000
M6 20.1 8040 10000 12000 16000 20000 24000
M8 36.6 14600 18300 22000 29000 36500 43000
M10 58 23200 29000 35000 46000 58000 69500
M12 84.3 33700 42100 50500 67000 84000 100000
M14 115 46000 57500 69000 92000 115000 138000
M16 157 62800 78500 94000 125000 157000 188000
M18 192 76800 98000 115000 154000 192000 230000
M20 245 98000 122000 147000 196000 245000 294000
M22 303 121000 151000 182000 242000 303000 364000
M24 353 141000 175000 212000 282000 353000 423000
M27 459 184000 230000 276000 367000 459000 550000
M30 561 224000 280000 336000 448000 561000 673000
M33 694 278000 347000 416000 555000 694000 833000
M36 817 327000 408000 490000 653000 817000 980000
M39 976 390000 488000 585000 780000 976000 1170000
M42 1120 448000 560000 672000 896000 1120000 1340000
M45 1300 520000 650000 780000 1040000 1300000 1560000
M48 1470 588000 735000 882000 1180000 1470000 1760000
M52 1760 704000 880000 1060000 1410000 1760000 2110000
  • Proof load = Stress under proof x tensile stress area of bolt
  • For stress under proof load
  • Nuts with a specified proof load above 500 000 N force may be exempted from proof load testing.

Tolerances on the standard nominal lengths of bolts and screws

Nominal length I Tolerance Nominal length I Tolerance
5 ±0.24 90 ±0.70
6 ±0.24 -95 ±0.70
-7 ±0.29 100 ±0.70
8 ±0.29 (105) ± 0.70
-9 ±0.29 110 ±0.70
10 ±0.29 -115 ±0.70
-11 ±0.35 120 ±0.70
12 ±0.35 -125 ±0.80
14 ±0.35 130 ±0.80
16 ±0.35 140 ±0.80
-18 ±0.35 150 ±0.80
20 ±0.42 160 ±0.80
-22 ±0.42 170 ±0.80
25 ±0.42 180 ±0.80
-28 ±0.42 190 ±0.925
30 ±0.42 200 ±0.925
-32 ±0.50 220 ±0.925
35 ±0.50 240 ±0.925
-38 ±0.50 260 ±1.05
40 ±0.50 280 ±1.05
45 ±0.50 300 ±1.05
50 ±0.50 325 ±1.15
55 ±0.60 350 ±1.15
60 ±0.60 375 ±1.15
65 ±0.60 400 ±1.15
70 ±0.60 425 ±1.25
75 ±0.60 450 ±1.25
80 ±0.60 475 ±1.25
85 ±0.70 500 ±1.25
  • Lengths shown in brackets are non-preferred.
  • See also Annex D.

Thread tolerance classes

Product Tolerance class
Bolts and screws 6g
Nuts (faced) 6H
Nuts (used with galvanized bolts) GAZ (in accordance with BS ISO 965-5)

Basis for standard thread lengths

Nominal length of boltI Length of thread b
Up to and including 125 mm 2d + 6 mm
Over 125 mm up to and including 200 mm 2d+12mm
Over 200 mm 2d + 25 mm

ISO metric precision hexagon bolts and screws

Nominal size and thread diameter d Pitch of (thread series) Thread runout a max. Diameter of shank d Width across flats s Width across corners e Diameter of washer face d
max. min. max. min. max. min. max. min.
M1.6 0.35 0.8 1.6 1.46 3.2 3.08 3.7 3.48  - -
M2 0.4 1 2 1.86 4 3.88 4.6 4.38  -  -
M2.5 0.45 1 2.5 2.23 5 4.88 5.8 5.51  -  -
M3 0.5 1.2 3 2.86 5.5 5.38 6.4 6.08 5.08 4.83
M4 0.7 1.6 4 3.82 7 6.85 8.1 7.74 6.55 6.3
M5 0.8 2 5 4.82 8 7.85 9.2 8.87 7.55 7.3
M6 1 2.5 6 5.82 10.0 9.78 11.5 11.05 9.48 9.23
M8 1.25 3 8 7.78 13.0 12.73 15.0 14.38 12.43 12.18
M10 1.5 3.5 10 9.78 17.0 16.73 19.6 18.9 16.43 16.18
M12 1.75 4 12 11.73 19.0 18.67 21.9 21.1 18.37 18.12
(M14) 2 5 14 13.73 22 21.67 25.4 24.49 21.37 21.12
M16 2 5 16 15.73 24 23.67 27.7 26.75 23.27 23.02
(M18) 2.5 6 18 17.73 27 26.67 31.2 30.14 26.27 26.02
M20 2.5 6 20 19.67 30.0 29.67 34.6 33.53 29.27 28.8
(M22) 2.5 6 22 21.67 32 31.61 36.9 35.72 31.21 30.74
M24 3 7 24 23.67 36 35.38 41.6 39.98 34.98 34.51
(M27) 3 7 27 26.67 41 40.38 47.3 45.63 39.98 39.36
M30 3.5 8 30 29.67 46 45.38 53.1 51.28 44.98 44.36
(M33) 3.5 8 33 32.61 50 49.38 57.7 55.8 48.98 48.36
M36 4 10 36 35.61 55 54.26 63.5 61.31 53.86 53.24
(M39) 4 10 39 38.61 60 59.26 69.3 66.96 58.86 58.24
M42 4.5 11 42 41.61 65 64.26 75.1 72.61 63.76 63.04
(M45) 4.5 11 45 44.61 70 69.26 80.8 78.26 68.76 68.04
M48 5 12 48 47.61 75 74.26 86.6 83.91 73.76 73.04
(M52) 5 12 52 51.54 80 79.26 92.4 89.56 - -
M56 5.5 19 56 55.54 85 84.13 98.1 95.07 - -
(M60) 5.5 19 60 59.54 90 89.13 103.9 100.72 - -
M64 6 21 64 63.54 95 94.13 109.7 106.37 - -
(M68) 6 21 68 67.54 100 99.13 115.5 112.02 - -
  • Sizes shown in brackets are non-preferred

ISO metric precision hexagon bolts and screws

Nominal size and thread diameter d Depth of washer face C Transition diameter da max. Radius under head r Height of head k Eccentricity of head max. Eccentricity of shank and split pin hole to the thread max.
max. min. max. min.
M1.6 - 2 0.2 0.1 1.23 0.98 0.18 0.14
M2 - 2.6 0.3 0.1 1.53 1.28 0.18 0.14
M2.5 - 3.1 0.3 0.1 1.83 1.58 0.18 0.14
M3 0.1 3.6 0.3 0.1 2.13 1.9 0.18 0.14
M4 0.1 4.7 0.35 0.2 2.93 2.68 0.22 0.18
M5 0.2 5.7 0.35 0.2 3.66 3.35 0.22 0.18
M6 0.3 6.8 0.4 0.25 4.15 3.85 0.22 0.18
M8 0.4 9.2 0.6 0.4 5.65 5.35 0.27 0.22
M10 0.4 11.2 0.6 0.4 7.18 6.82 0.27 0.22
M12 0.4 14.2 1.1 0.6 8.18 7.82 0.33 0.27
(M14) 0.4 16.2 1.1 0.6 9.18 8.82 0.33 0.27
M16 0.4 18.2 1.1 0.6 10.18 9.82 0.33 0.27
(M18) 0.4 20.2 1.1 0.6 12.22 11.79 0.33 0.27
M20 0.4 22.4 1.2 0.8 13.22 12.79 0.33 0.33
(M22) 0.4 24.4 1.2 0.8 14.22 13.79 0.39 0.33
M24 0.5 26.4 1.2 0.8 15.22 14.79 0.39 0.33
(M27) 0.5 30.4 1.7 1 17.22 16.79 0.39 0.33
M30 0.5 33.4 1.7 1 19.26 18.74 0.39 0.33
(M33) 0.5 36.4 1.7 1 21.26 20.74 0.39 0.39
M36 0.5 39.4 1.7 1 23.26 22.74 0.46 0.39
(M39) 0.6 42.4 1.7 1 25.26 22.74 0.46 0.39
M42 0.6 45.6 1.8 1.2 26.26 25.74 0.46 0.39
(M45) 0.6 48.6 1.8 1.2 28.26 27.74 0.46 0.39
M48 0.6 52.6 2.3 1.6 30.26 29.74 0.46 0.39
(M52) - 56.6 2.3 1.6 33.21 32.69 0.46 0.46
M56 - 63 3.5 2 35.31 34.69 0.54 0.46
(M60) - 67 3.5 2 38.31 37.69 0.54 0.46
M64 - 71 3.5 2 40.31 39.69 0.54 0.46
(M68) - 75.0 3.5 2 43.31 42.69 0.54 0.46
  • All true radius is not essential providing that the curve is smooth and lies wholly within the maximum radius, determined from the maximum transitional diameter and the minimum radius specified.

ISO metric precision hexagon nuts and thin nuts

Nominal size and thread diameter d Pitch of thread (coarse pitch series) Width across flats s Width across corners e Thickness of normal nut m Tolerance on squareness of thread to face of nut Eccentricity of hexagon Thickness of thin nut t
max. min. max. min. max. min. max. max. max. min
M1.6 0.35 3.2 3.08 3.7 3.48 1.3 1.05 0.05 0.14  -  -
M2 0.4 4 3.88 4.6 4.38 1.6 1.35 0.06 0.14  -  -
M.2 0.45 5 4.88 5.8 5.51 2 1.75 0.08 0.14 -  - 
M3 0.5 5.5 5.38 6.4 6.08 2.4 2.15 0.09 0.14 -   -
M4 0.7 7 6.85 8.1 7.74 3.2 2.9 0.11 0.18 -   -
M5 0.8 8.00 7.85 9.2 8.87 4 3.7 0.13 0.18 -   -
M6 1 10 9.78 11.5 11.05 5 4.7 0.17 0.18 -   -
M8 1.25 13 12.73 15 14.38 6.5 6.14 0.22 0.22 5 4.7
M10 1.5 17 16.73 19.6 18.9 8 7.64 0.29 0.22 6 5.7
M12 1.75 19 18.67 21.9 21.1 10 9.64 0.32 0.27 7 6.64
(M14) 2 22 21.67 25.4 24.49 11 10.57 0.37 0.27 8 7.64
M16 2 24 23.67 27.7 26.75 13 12.57 0.41 0.27 8 7.64
(M18) 2.5 27 26.67 31.2 30.14 15 14.57 0.46 0.27 9 8.64
M20 2.5 30 29.67 34.6 33.53 16 15.57 0.51 0.33 9 8.64
(M22) 2.5 32 31.67 36.9 35.72 18 17.57 0.54 0.33 10 9.64
M24 3 36 35.38 41.6 39.98 19 18.48 0.61 0.33 10 9.64
(M27) 3 41 40.38 47.3 45.63 22 21.48 0.7 0.33 12 11.57
M30 3.5 46 45.38 53.1 51.28 24 23.48 0.78 0.33 12 11.57
(M33) 3.5 50 49.38 57.7 55.8 26 25.48 0.85 0.39 14 13.57
M36 4 55 54.26 63.5 61.31 29 28.48 0.94 0.39 14 13.57
(M39) 4 60 59.26 69.3 66.96 31 30.38 1.03 0.39 16 15.57
M42 4.5 65 64.26 75.1 72.61 34 33.38 1.11 0.39 16 15.57
(M45) 4.5 70 69.26 80.8 78.26 36 35.38 1.2 0.39 18 17.57
M48 5 75 74.26 86.6 83.91 38 37.38 1.29 0.39 18 17.57
(M52) 5 80 79.26 92.4 89.56 42 41.38 1.37 0.46 20 19.48
M56 5.5 85 84.13 98.1 95.07 45 44.38 1.46 0.46 - -
(M60) 5.5 90 89.13 103.9 100.72 48 47.38 1.55 0.46 - -
M64 6 95 94.13 109.7 106.37 51 50.26 1.63 0.46 - -
  • Sizes shown in brackets are non-preferred
  • For tolerances on squareness of thread to face of nut

ISO metric precision hexagon slotted nuts and castle nuts

Nominal size and thread diameter d Diameter d2 Thickness h Lower face of nut to bottom of slot m Width of slot n Radius (0.25n) r Nominal size of split pin and nominal drill Eccentricity of the slots max.
max. min. max. min. max. min. max. min. min.
M4 - - 5 4.7 3.2 2.9 1.45 1.2 0.3 It is intended to provide appropriate values in this column once International agreement has been reached on metric series split cotter pins 0.18
M5 - - 6 5.7 4 3.7 1.65 1.4 0.35 0.18
M6 - - 7.5 7.14 5 4.7 2.25 2 0.5 0.18
M8 - - 9.5 9.14 6.5 6.14 2.75 2.5 0.625 0.22
M10 - - 12 11.57 8 7.64 3.05 2.8 0.7 0.22
M12 17 16.57 15 14.57 10 9.64 3.8 3.5 0.875 0.27
(M14) 19 18.48 16 15.57 11 10.57 3.8 3.5 0.875 0.27
M16 22 21.48 19 18.48 13 12.57 4.8 4.5 1.125 0.27
(M18) 25 24.48 21 20.48 15 14.57 4.8 4.5 1.125 0.27
M20 28 27.48 22 21.48 16 15.57 4.8 4.5 1.125 0.33
(M22) 30 29.48 26 25.48 18 17.57 5.8 5.5 1.375 0.33
M24 34 33.38 27 26.48 19 18.48 5.8 5.5 1.375 0.33
(M27) 38 37.38 30 29.48 22 21.48 5.8 5.5 1.375 0.33
M30 42 41.38 33 32.38 24 23.48 7.36 7 1.75 0.33
(M33) 46 45.38 35 34.38 26 25.48 7.36 7 1.75 0.39
M36 50 49.38 38 37.38 29 28.48 7.36 7 1.75 0.39
(M39) 55 54.26 40 39.38 31 30.38 7.36 7 1.75 0.39
M42 58 57.26 46 45.38 34 33.38 9.36 9 2.25 0.39
(M45) 62 61.26 48 47.38 36 35.38 9.36 9 2.25 0.39
M48 65 64.26 50 49.38 38 37.38 9.36 9 2.25 0.39
(M52) 70 69.26 54 53.26 42 41.38 9.36 9 2.25 0.46
M56 75 74.26 57 56.26 45 44.38 9.36 9 2.25 0.46
(M60) 80 79.26 63 62.26 48 47.38 11.43 11 2.75 0.46
M64 85 84.13 66 65.26 51 50.26 11.43 11 2.75 0.46
M68 90 89.13 69 68.26 54 53.26 11.43 11 2.75 0.46
  • For width across flats and widths across corners,
  • Sizes shown in brackets are non-preferred

Strength grade designation of steel nuts

Strength grade designation 4 5 6 8 10 12
Proof load stress MPa 400 500 600 800 1000 1200

Finishes

Product type Finishes
Heat-treated bolts and screws Components heat-treated after manufacture shall be dull black, although the manufacturer might machine some of the surfaces of the larger size bolts and screws after heat treatment.
Bright finished bolts and screws This term is used to describe bolts and screws which are finished bright on all surfaces or which have a finish on the hexagon, produced by bright drawing.
Nuts These can be bright on all surfaces or dull black when heat-treat ed.
Other finishes If the purchaser requires bolts, screws or nuts (or other material) to be coated, the type of coating required should be stated in their enquiry and order, where reference should be made to the appropriate British Standard, i.e. BS EN 150 4042, BS 7371-6 or BS EN 150 10684.
  • NOTE If steel bolts, screws or nuts are required finished bright all over, this is usually stated in the enquiry and order

Marking of nuts

Strength grade designation 8 10 12
Marking symbol 181 1101 1121

BS 3692 Bolting Surface Treatment Specifications

BS 3692 Bolting Components Marking

Product Shall be Marked with our manufacturing trade mark "TorqBolt" or "TB" along with the designated Grade.
Grade and manufacturer’s identification symbols shall be applied to one end of studs and to the heads of bolts and screws of all sizes. (If the available area is inadequate, the grade symbol may be marked on one end and the manufacturer’s identification symbol marked on the other end.) For bolts and screws smaller than 1⁄4 in. [6 mm] in diameter and studs smaller than 3⁄8 in. [10 mm] in diameter and for 1⁄4 in. [6 mm] in diameter studs requiring more than a total of three symbols, the marking shall be a matter of agreement between the purchaser and the manufacturer.

ASME Dimensional Standards

BS 3692 Bolting Certifications

  • EN 10204 3.1
  • EN 10204 3.2
  • PED 2014/68/EC
  • MERKBLATT AD 2000 W2/W7/W10
  • API 20 E BSL 1/ BSL 2
  • NACE MR 0175
  • NACE MR 0103

BS 3692 Testing Standards

ASME Threading Specifications

BS 3692 Supplementary Requirements