The most common size router table insert plates are 9-1/4 x 11-3/4 inch with rounded corners. The radius of the rounded corners is usually 3/4 inch. Rockler's router table insert plates are different: 8-1/4 x 11-3/4 inch.
Buy the insert plate before you cut the hole, and remember to leave supports for the leveling screws.
Your title, "Lift router insert plates" is confusing, because I am not sure if you mean a "router lift" or a "router with a built-in lift."
A "router lift" is designed to clamp around a cylindrical router motor only (no router base). It allows you to control precise router bit height from the top of the router table. An insert plate is built-in. You size the cutout in your router table to match the plate, and use set screws to level it with the router table.
If you are buying a router lift, be sure it is compatible with your router motor. If you can afford a router lift, you may want to buy a good motor to go with it, one that is a good fit for the lift.
A "router with a built-in lift" is a router with a special feature that lets you mount the router and fixed base underneath a router table where you insert a crank handle through a drilled hole to the router and its base below. The handle lets you adjust router bit height from above like a true router lift. It won't have the same precision as a true router lift, but may be sufficient for some needs. Several manufacturers make routers with this feature.
Not all routers have built-in lifts, but you can use them in a router table anyway. The drawback is that you must reach underneath the table to make the router bit height adjustment. If you attach the router base to a flat insert plate, then you can lift out the plate+router and make the adjustment on a tabletop first, then put them back in the table, a less awkward approach.
Every router manufacturer seems to have a different screw hole arrangement for their router bases. You can buy a plain insert plate and drill it yourself. Some manufacturers make a variety of flat insert plates, predrilled for different brands of router bases.
Last edited by Tool Agnostic; 06-28-2020 at 01:03 PM.