Unfasten the locking device that holds the table together, if any. There may be a pair of mechanisms that unclasp, unhinge, turn or twist to release one half of the table from the other. These hand-operable devices are typically located on the underside of the table. Many tables have no fastening mechanism. Consult your product information for instructions specific to your table design.
Grasp one side or end of the table and pull until you see an opening at the table's center. If you want to pull both ends at once, you might need help from a friend or family member.
Drop the leaf gently into the opening in the table.
Ease the halves of the table back in toward the new leaf in the middle. In the end, no gaps should be apparent.
Tug gently on the slide-out end leaf that rests just beneath the top of the table.
Ease it out until no part of it is beneath the table's top.
Listen for the locking sound that indicates the leaf is securely extended. The sound is likely to be akin to a click or a snap.