Here is my smaller steady rest, for smaller diameters :
Front side :
Here is the base and how it is bolted to the bed :
The radial arms are pressed against the wood thanks to that rectangular piece of steel. It is tapped in the middle and it has two pins at each sides, that go into holes in the wood, to keep the arm radial alignment.
The roller is a ball bearing, simply glued with CA to the little post.