This support is made from red oak and glued and screwed together. It is about 1 1/8 thick with 5/8" hole drilled for the motor shaft to fit in.
It is made in three pieces and the 2 piece curve was cut to match the Dewalt router motor that I have. The 2 bolts go through the two halves to hold the router in place.
The piece in the back is used to stabilize the router support with wing nuts.
You can adjust the height by using adjustment on the radial arm saw or fine adjustments on the router motor.
Since it is on a radial arm saw you can fix the piece and move the router or as I am doing fix the router and move the piece.
Here is a little video on the router support: