Is this for the Freud? 4 machine screws (M8 would do, or whatever screws into the base plate, which you'll maybe remove anyway), countersunk into you router plate or whatever you are using. Just re-read your post, do you mean the plate? No screws, gravity does the job.
The way I understand it I buy a plate from Trend, remove the base plate from the router and screw the Trend one in it's place. This Trend plate then screws into the underside of the CRT Mk2 table - it's these screws for fixing the plate to the table I'm wondering about.
I would imagine it's something like an M6 or M8, but SWMBO has tidied up and I can't find the manual