01. Jul. 2020
3
Dynapac Training Academy Christian Langhorst
General Information
Overview Tightening Torques
Comments
General values for screw connections with metric standard and fine thread without
specified tightening torque. EN4369K 2005.12.15
CAUTION! No automatic change to this document if the standard changes!
General
This standard gives recommendation for the selection of tightening torques for normal screw
connections if no specific tightening torque is specified. The tightening force of the screw
connections is ensured via the tightening torque.
Normal screw connections are designed for a 75% degree of utilization of the screw material and a
maximum deviation of 25% of the resulting tightening torque. Self-locking threads are not taken into
account in the calculated tightening torques.
For non-lubricated and lightly oiled connections an equal friction value is assumed, for the thread of
µg = 0.15 and under the head or nut of µg = 0.125.
Coefficients of friction of µg = 0.11 and under the head or nut of µg = 0.11 are assumed for
connections with Molykote.
If there are special requirements for a screw connection, the tightening torque must be calculated
and given the conditions with regard to lubrication, waxing, surface treatment on the drawing.
For screw connections with specified requirements, see AC-STD 4369: 01
Application
The information given in this standard has been limited as follows:
AC-STD 3511 K applies to screws and nuts with large metric threads.
Strength classes 8.8, 10.9 and 12.9 for screws, nuts and thread material must correspond to the
corresponding strength class (AC-STD 4142K and AC-STD 4143K)
Tolerance classes 6G and 6H for metric screws and nuts accordingly, see AS-STD 3513K.
Hexagon bolts and nuts of normal wrench size.
Black or galvanized, non-oiled, lightly oiled or Molykote lubricated screws and nuts.
Bearing surfaces (under screw head and nut) with the help of at least 200HB, a surface roughness Ra
3.2 µm and through holes according to AC-STD 4361 K, medium series.
Information on drawings
The tightening torques for normal connections according to Tables 1 to 3 can be specified in the
manufacturing documents by the general reference to this standard.
Example: Unless otherwise stated, tightening torques acc. To AC-STD 4369 K.
