I used a forstner bit to remove about 1/16"
of wood to keep the tee-nuts flush with the surface of the oak.
Pictured here is a tee-nut, bit, and a 10-24 bolt and
washer used to bolt the insert to the main table from
underneath. Countersinking the nut may be unnecessary
because this will be covered by the 1/4" foam, but I didn't
want to take any chances, because the foam will hard to
remove later.