Mitsubishi Melsec-Q Series User Manual page 242

For use in an environment with particularly frequent vibrations and/or shock, secure the module to
the base with screws. The applicable screw size is M4(0.16) 0.7(0.03) 12mm (0.47 inches).
Refer to the figure on the right.
CAUTION
10 - 28
To mount a module, Insert the module fixing projection(s) into the fixing
hole(s) in the base unit and press the module until it snaps into place.
Incorrect mounting may cause malfunction, failure, or a drop of the
module.
When using in an environment of frequent vibrations, secure the module
with a screw.
Tighten the screw within the specified torque range.
Undertightning can cause drop of the screw, circuit or malfunction.
Overtightning can damage the screw and/or module, resulting in drop,
short circuit, or malfunction.