You really only need something to keep the out feed end of the insert from lifting if the rising teeth of the blade should catch on it. You really don't want to have the blade throw the insert at you. Otherwise, the insert that you make should remain in place with gravity. I install a small roll pin in the out feed end of the inserts that I make for my Unisaw, and thread four 1/4-28 holes in the four support locations to level the insert and install set screws. The finer 1/4-28 threads tend to not back off from vibration like the coarse 1/4-20 threads do. My inserts are made from scrap Corian, HDPE, or Baltic Birch plywood, basically whatever I have on hand, and I usually make 6-10 at a time, leaving them as blanks until I need to use them. Then I make the blade cut with the blade that it will be used with. After it is cut, I write the blade details on the bottom of the insert and I will only use the insert for the blade that it is matched to. When the slot wears or the insert is somehow damaged, I discard it and make a replacement from one of the blanks on hand. I consider a good zero clearance insert to be a necessity for clean, accurate, splinter free, and safe cutting of my project parts, and I replace them often.
I have made zero clearance inserts for many different saws, and the Unisaws are some of the easiest to make because they are basically just a big oval of 1/2" thick material. The older Delta Contractor saws use the same insert The Ridgid and DeWalt contractor saws and the Ryobi BT3000 and 3100 are some of the harder ones to make because of the irregular shapes that the lower portion of the inserts require. The easiest way to make these is to find a material of the correct thickness to make the top of the insert and then use a thicker material to make the irregularly shaped lower part, cutting the irregular shape with a scroll saw or band saw., Then glue the two layers together. Baltic Birch plywood usually works best for these because it is available in many different thicknesses and can be purchased in small pieces from hobby and scroll saw supply houses. On Baltic Birch inserts, a coat of polyurethane followed by a coat of paste wax on the top usually provides a smooth enough surface, with the poly providing a seal to keep humidity from affecting the fit of the insert in the saw opening,
Central North Carolina