Weidmuller GPRS Alarm Unit - Manual (Page 75)

Hardware
5-73
When mounting a top-hat rail adapter on the rear of the housing, it
is imperative to observe the correct position of the retaining
spring:
Plastic variant: Retaining spring at the bottom
Aluminium variant: Retaining spring at the top
CAUTION: Incorrect mounting will reduce the retaining force of the
top-hat rail adapters.
Only use the original screws of the top-hat rail; longer screws will
damage the electronics of your IE-GPRS-I/O. The screws to be
used are M3 x 8 round head for adapters with plastic insert and M3
x 4 countersunk head for aluminium adapters.
NOTE