Every woodworker uses their router table's top for something other than routing - project assembly, sanding station, storage - and everyone eventually gets some foreign object into an unused router.

This solid steel insert is identical to your other MagnaLOCK Rings except that there's no router bit opening.  When you're not using your router, this insert keeps out sawdust, small tools, loose hardware, and everything else that you don't want dropped into the motor. 

This is a must-have item if your router setup is built into a table or saw work bench, and it will save you aggravation at any router table that uses an Incra Router Plate or Router Lift.