Because we’re not experts we built this from one end to the other. This isn’t the most efficient way to do it, but it will ensure that rail is firm and doesn’t have any slop in it from mis-measurement.
Place the flange so that you can see your mark in the middle of the circle.
Mark the two hole locations with the marker.
Drill your holes
Put flange in place.
Screw in Concrete anchors.
We needed to use a rachet on the screws to get them seated all the way.