Construction:

After several test models I settled on a 13: radius with a 3" offset for my wind indicator.  This was a good compromise between readability, sensitivity and portability.

The 2" piece of 3/8" channel is used to strengthen cross member and provide support for  3/8" center  rod.  I uses pop rivets to attach this piece to the 1/4" channel, but small bolts or self tapping screws will work just as well.   I drill a 1/4" hole through both pieces and elongate with a file to 3/8" for the flattened center rod.
The 3 1/2" 3/8" channel provides additional support to keep everything square and supports the pivot shaft. 
The 3/8" center rod is flattened on each side for 1 1/4" to a thickness of 1/4".  Drill 1/8" hole 1" deep in the top end to hold the 9 1/2" support rod.

Right picture shows the Brass Union and the shaft that is a key component of my 'Wind Indicators'.

I make spacers out of telescoping portable TV antennas.  I find the right size tube and cut to a length that will keep the Union and counter weight clear of flag and stand.

Detail of Shaft & Union