Zero Clearance insert for the R225 mitre saw from evolution power tools. It has a dust box on the bottom with an opening at one end. This prevents dust from falling out the underneath of the saw and encourages dust to be flung up from the insert and towards the dust shoot. (this part still needs verifying. 

This is designed to be a friction fit so its slightly overside and the dust box requires a bit of sanding to make it fit as tight as possible. 

The original insert is a bit hard to remove without seeing how it attaches. You need to unhook the back of the insert and then slide the whole insert backwards, then it should just lift out.