Phenolic is the material of choice for mounting plates, or aluminum. Either way 1/4" is the thickness you are looking for. Both will flex a bit with a 7518. I am mounting my 7518 on a Rousseau plate for easy swapping in my tables. The Rousseau plate has a built in curve to the top surface that flatens out with the weight of a router. Add to this the ability to mount guide bushings in the center, easy opening size changes, the safety pin, corner snuggers and levelers. The $44.95 price tag from Woodcraft is very reasonable for this well thought out design.
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