Sealyons

I have a Mitsubishi FX5UC-32MR/DS-TS PLC and seem to be having difficulty inserting ferruled wires into the I/O connectors. I'm using 18g wire with associated ferrules but when I press on the cage clamps and insert the ferrule it doesn't catch. I've read through the instructions and it appears the wire cross section is fine and the clamps are designed to take ferrules but I can't get it to catch. It doesn't appear to provide info on the specs of for the ferrules. Is there some trick that I'm not seeing? Appreciate any help. Thanks. 

Yes, I finally found the wire gauge info on page 93. I was attempting to use 18awg wire with insulated ferrules. Obviously a bad choice. Switched to non-insulating ferrules and all is good. Appreciate the reply. Thanks.