Rather than mess with gluing up plastic laminate, I use a piece of laminate flooring when making zero-clearance inserts. Laminate flooring is great because it’s stiff, with a nice slick surface. It’s between 1/4-in. and 3/8-in. thick, which is just right for inserts. It also saws and routs nicely.
I bought a couple of sample pieces of laminate flooring for $6 per 8-in. by 48-in. piece. You can find it at home centers and flooring stores. Each plank makes four inserts.
I used #10-24 by 3/8-in.-long socket-head setscrews for the leveling screws rather than flat-head screws. I prefer setscrews because I don’t have to drill a countersink. Some saws require a 1/2-in. long setscrew because the support flanges that the insert rests on are lower. To determine the screw’s size, measure from the top of your saw table down to the support flange. Buy setscrews that are about 1/16-in. to 1/8-in. shorter than this measurement. You can buy socket setscrews at most hardware stores for about 25 cents each.