Personnaly I have fitted heavier contacts, onto patio doors like that. Check
for gap specification and try the magnet and contact with a multimeter
before actually fitting them to the door. Other alternative is to buy a
couple of the same contact, screw the reed switch on, and then use two or
three of the same magnets built on top of each other on the actual door.
Holes line up and using the correct length of screw its fine :-))