Tightening torques for stainless steel bolts

Introduction

Minimum breaking torque (M b,min) for austenitic grade bolts and screws between M 1.6 and M 16 (course threads) are shown in table 4 of BSENISO 3506-1:1997. This shows torque values in Nm for property classes 50, 70 and 80 as shown in the table below. This applies to 'grades' A1, A2, A3, A4 and A5. Tightening torque values are not given in this standard.

Minimum breaking torque values

Torque values are not given for martensitic (C1, C3, C4) or ferritic (F1) grades. The standard states that these values are to be agreed between manufacturer and user.

  Min breaking torque Nm for property class
  50 70 80
M1.6 0.15 0.2 0.24
M2 0.3 0.4 0.48
M2.5 0.6 0.9 0.96
M3 1.1 1.6 1.8
M4 2.7 3.8 4.3
M5 5.5 7.8 8.8
M6 9.3 13 15
M8 23 32 37
M10 46 65 74
M12 80 110 130
M16 210 290 330

Maximum tightening torque, yield loads and failure loads for austenitic stainless steel fasteners

Tightening torques, yield loads and failure loads are not given in the BSENISO 3506-1:1997 standard. Some data is available however on the Bufab UK web site.

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