Step 16: Trial the extension runners
Taper the protruding end of each runner (i) (as shown in the drawing below) to ensure easy insertion into the notches in the table (the sliding runner holes).
Sand, plane, or saw the taper on each runner (i) until they slide in and out with ease.
Trial and trial again makes perfect.
Step 17: Commence the extensions
Insert the runners (i) into the notches and ensure that they are parallel.
Place the first extension-top board (h) in place on top of the runners. Place it up against the table and make the ends flush with each side of the table.
Take a pencil and mark the position of the runners on the extension-top board (from underneath), and mark the position of the extension-top board on the runners (from above).
Step 18: Continue with the extensions
Continuing from step 17, lay the other two extension-top boards in place at each end of the table.
Place them against each other and in line with one another (i.e. flush at the ends).
Now mark them in the same way as the first board was marked - as described in step 17.
Ensure that throughout steps 17 and 18, the runners are parallel at all times while marking.