Additional Info here
Grade 2 Contact, Normally Open, Surface, Single Reed, 6 Terminal, Tamper
D75 is a standard Grade 2 surface contact.
6 wire clamping screw down terminals are provided on the PCB – two for the switch, two for tamper and two unlinked spares.
The tamper on this contact is provided by a sprung microswitch, which will detect removal of the lid.
This contact is Normally Open (N/O) – The circuit through the contact is complete until the magnet is moved close by. With the magnet in close proximity, the circuit through the contact is broken.
Supplied with fitting screws.