Router holder, back side
1 1/4" #8 wood screws
In the lift that I built, I had to drill a hole in this błock to make room for the end of the threaded rod.
I slightly modified the dimensions in this plan to make this hole unecessary.
Two smali pan head sheet metal screws hołd the nut in place.
Glued joint
Drill a hole the size of the flat-to-flat sitance of your 3/8" nut, then chisel rectangular. Also drill 7/16" through the błock.
You can also use a T-nut here, but you will have to file down one side of it to make it fit.