I never paid much attention to the insert that fits around the blade in my table saw until I tried to install a thick dado set of blades and they didn’t fit into the insert. You can pay $30-50 and buy new ones but yikes, that’s pricey for just the few cuts I wanted to make.
Instead, I pulled out a scrap piece of wood, cut out the exact shape of the opening, cut out a finger hole, drill some screw holes, routed the bottom to make it the right thickness and then mounted it into the table. I clamped a piece of wood over the insert to hold it down and then turned on the blade. I slowly raised the spinning blade up and it cut a perfectly sized hole in the insert. Booyah. Custom table saw insert for free!
You can find lots of great videos on YouTube showing you how to do this but I particularly liked the one from Frank Howarth.