Tightening torque and force

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When assembling stainless steel joints, a very low revolution screw-driving machine is required, or the screws should be tightened by hand. Punching screw-driving machines should not be used.

MoS2 lubricant or similar is recommended in unfavorable assembly conditions. If considerable thread galling problems occur when assembling, please contact our technical service.

Class M3 M4 M5 M6 M8 M10 M12 M14 M16 M18 M20 M24 M27 M30 M36
Tightening torque Nm ¹ Bumax Ultra 159 ³ 2.6 6.1 12 21 50 99 172 273 420
Bumax DX/SDX 129 2.1 4.9 9.8 16 40 79 137 218 336
Bumax DX/SDX 109 1.7 4.1 8.1 14 34 66 115 182 280 390 547 840
BUMAX 109 1.7 4.1 8.1 14 34 66 115 182 280 344 547
BUMAX 88 1.3 2.9 5.7 10 25 47 82 129 198 275 385 665 960 1310 2280
BUMAX Lock 6.6 12 29 54 94 148 228 317 442 765
80 1.2 2.7 5.4 9 22 44 76 121 187 261 364 629 909 1240 2160
70 0.9 2 4 7 17 33 57 91 140 195 273 472 682 930 1620
Class M3 M4 M5 M6 M8 M10 M12 M14 M16 M18 M20 M24 M27 M30 M36
Preload applied kN² Bumax Ultra 159 ³ 4.4 7.7 12 18 32 51 74 100 138
Bumax DX/SDX 129 3.5 6.2 10 14 26 41 59 81 110
Bumax DX/SDX 109 2.9 5.2 8.6 12 21 34 49 67 92 112 143 207
BUMAX 109 2.9 5.2 8.6 12 21 34 49 67 92 112 143
BUMAX 88 2.1 3.6 5.9 8.4 15 24 35 48 65 80 102 146 190 233 340
BUMAX Lock 5.9 8.4 15 24 35 48 65 80 102 181
80 2.0 3.4 5.5 7.8 14 23 33 45 61 76 96 138 179 219 319
70 1.5 2.6 4.2 5.9 11 17 25 34 47 57 72 103 134 164 239
Class M3 M4 M5 M6 M8 M10 M12 M14 M16 M18 M20 M24 M27 M30 M36
Failure load, min kN Bumax Ultra 159 ³ 7.5 13 21 30 55 87 127 173 236
Bumax DX/SDX 129 6 10.5 17 24 44 70 101 138 188
Bumax DX/SDX 109 5 8.8 14 20 36 58 84 115 157 192 245 353
BUMAX 109 5 8.8 14 20 36 58 84 115 157 192 245
BUMAX 88 4 7 11 16 29 46 67 92 126 154 196 282 367 449 654
BUMAX Lock 11 16 29 46 67 92 126 154 196 282
80 4 7 11 16 29 46 67 92 126 154 196 282 367 449 654
70 3.5 6.1 9.9 14 26 41 59 81 110 134 172 247 321 393 572
Class M3 M4 M5 M6 M8 M10 M12 M14 M16 M18 M20 M24 M27 M30 M36
Yield load, min kN 15.9 ³ 6.8 12 19 27 49 78 114 155 212
12.9 ³ 5.4 9.5 15 21 39 62 91 124 170
Bumax DX/SDX 109 4.5 8 13 18 33 52 76 104 141 173 221 318
BUMAX 109 4.5 8 13 18 33 52 76 104 141 173 221
BUMAX 88 3.2 6 9 13 23 37 54 74 100 123 157 226 294 359 523
BUMAX Lock 9 13 23 37 54 74 100 123 157 226
80 3 5 8 12 22 35 51 69 94 115 147 212 275 337 490
70 2.2 4 6 9 16 26 38 52 71 86 110 159 207 253 368
Nominal stress
area mm²		 5.03 8.78 14.2 20.1 36.6 58.0 84.3 115 157 192 245 353 459 561 817
Pitch of thread 0.5 0.7 0.8 1.0 1.25 1.5 1.75 2.0 2.0 2.5 2.5 3.0 3.0 3.5 4.0

 

UNC

Class 1/4-20 UNC 5/16-18 UNC 3/8-16 UNC 1/2-13 UNC 5/8-11 UNC 3/4-10 UNC 7/8-9 UNC 1-8 UNC
Tightening torque Nm ¹ BUMAX 88 11.0 22.0 39.0 95.0 188.0 329.0 527.0 789.0
80 10.0 21.0 37.0 89.0 175.0 308.0 493.0 737.0
70 7.7 16.0 28.0 66.0 131.0 231.0 369.0 553.0
50 3.6 7.3 13.0 31.0 61.0 108.0 172.0 258.0

 

Class 1/4-20 UNC 5/16-18 UNC 3/8-16 UNC 1/2-13 UNC 5/8-11 UNC 3/4-10 UNC 7/8-9 UNC 1-8 UNC
Preload applied kN² BUMAX 88 8.7 14.3 21.1 38.7 61.7 91.2 125.9 165.2
80 8.0 13.2 19.5 35.7 56.9 84.2 116.2 152.5
70 6.0 9.9 14.6 26.8 42.7 63.2 87.2 114.4
50 2.8 4.6 6.8 12.5 19.9 29.5 40.7 53.4

 

Class 1/4-20 UNC 5/16-18 UNC 3/8-16 UNC 1/2-13 UNC 5/8-11 UNC 3/4-10 UNC 7/8-9 UNC 1-8 UNC
Failure load, min kN BUMAX 88 17.0 28.0 41.5 75.9 121.0 179.0 247.0 325.0
80 17.0 28.0 41.5 75.9 121.0 179.0 247.0 325.0
70 14.3 23.6 35.0 64.1 102.2 151.2 208.6 273.7
50 10.2 16.9 25.0 45.7 73.0 108.0 149.0 195.5

 

Class 1/4-20 UNC 5/16-18 UNC 3/8-16 UNC 1/2-13 UNC 5/8-11 UNC 3/4-10 UNC 7/8-9 UNC 1-8 UNC
Yield load, min kN BUMAX 88 13.1 22.4 33.2 60.8 96.9 143.4 197.9 256.6
80 12.3 20.3 30.0 54.9 87.6 129.6 178.8 234.6
70 9.2 15.2 22.5 41.2 65.7 97.2 134.1 175.9
50 4.3 7.1 10.5 19.2 30.7 45.4 62.6 82.1
Nominal stress
area mm²		 20.5 33.8 50.5 91.5 146.0 216.0 298.0 391.0

Bumax Hard Taptite, thread forming screws

Class M3 M4 M5 M6 M8 M10
Tightening torque Nm Hard Taptite 1.3 3 6 12 25 49
Thread cutting torque Nm Hard Taptite 0.7 1.8 3.5 8 15 28
Breaking torque, min Nm Hard Taptite 4.5 7.9 13 20 30 52

Table footnotes

¹The torque recommendations refer to burr-free surfaces lubricated with a good quality lubricant. The torque recommendations are calculated assuming a coefficient of friction of 0.14, which requires a good quality lubricant. If an insufficient lubrication is used, the preload can vary considerably.

²The Preload applied kN is calculated as 65% of Rp0.2 but in practice the value can be expected to vary between 50-80% (+/- 23%).

³Typical strength level for BUMAX® Ultra “The world’s strongest stainless steel fastener” is 159 (Tensile strength min 1500 MPa/ Yield strength min 1350 MPa). All BUMAX Ultra fasteners are custom made to meet the requirements of individual applications and can be delivered with different mechanical properties, sometimes with even higher strength than class 159. BUMAX® Ultra is an advanced engineering grade and close technical support is provided by BUMAX customer projects in order to develop the desired end solution. Contact BUMAX sales representative for more information.

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