XALK boxes can accommodate a maximum of 3 contacts in any configuration.
Please bear in mind this maximum particularly when adding to an already complete part.
E.g. XALK178F is a complete enclosed emergency stop pushbutton, that comes with 2 normally closed (N/C) base mounted contact blocks. You may add a single additional contact block of either the normally open (N/O) or normally closed (N/C) type, to achieve the maximum of 3 contacts.
N/O contact: ZENL1111
N/C contact: ZENL1121