Well I don't use that type of control but if I relate what I see to a horizontal airplane control like I used then I would say that is a detachable leg bar. When the bar is on the curved wire it can pivot at it axis.  That means you could make the puppet walk simply by grabbing one side of the bar and moving it up or down.  I think in the profile it is showing that this bar can actually be removed in order to get more movement. 

On a horizontal airplane control I always did this in order to walk the puppet I removed the leg bar and manipulated it. I felt this gave me more range of movement but it means you loos that hand for other manipulation.

Many puppeteers and builders prefer the vertical design you see in the picture because they want to be able to nudge the leg bar with the same hand they are holding the main control in to make the puppet walk. This leaves the other hand free to manipulate other strings while walking. It is just a matter of preference.

Hope folks don't miss my inquiry on #8 above.  Really appreciate your insight folks.

Sorry I missed that post.

Coat hanger could work but might be a bit thick. I often use what is called piano or spring wire. Don't be confused that it is just the wire used in pianos. http://www.asada-metal.com/seihinE/#2 It is a hardened wire that is very hard to bend or cut. Hardware stores often carry it if they are a mom and pop smaller store but I've even found it in Home Depot. You can also find it in hobby stores that cater to model making often.

Like I said it is very strong, even the thinner gauges, and difficult to bend. For something the gauge of coat hanger I would have to put one end in the vice and then bend it with vice grips. It is ideal for controls both for it's strength and for the fact that like it's alternate name it has "spring" or memory in it. I've used it for a simple rod puppet of butterflies... place a dozen or so butterflies with some weight in them on the end of wires and bundle them together and just a slight "jiggle" and you have a swarm flying about the stage.

Now before you ask me... I can't really give you a gauge. Never was good at remember those and I always just had a variety around that I used depending on my need. You would want something that was not quite as big as a coat hanger really or you are going to have to drill large holes in your wood pieces which just weakens it.

Thank you Shawn- it seems to me I read somewhere the ideal size piano wire is 3/32.  I never made the connection that this wire was being used for controllers.
Appreciate your feedback.

Here's a place that sells the Czech style vertical controllers... Not a huge fan of this type of controller myself, but that's a personal preference only.

http://puppetsinprague.eu/shop.html

I have a bunch of vertical controllers similar to the ones in the picture (reply #3). They are great to use, but make sure the wire is nice and strong. You will often want to manipulate one hand with the thumb of the hand you're holding the controller with. So you're pushing up on the wire close to where it joins the controller which requires a bit more force and pressure in a localised spot... I'd imagine it would be pretty easy to put a bit of a bend in the wire after repeated use if it wasn't sturdy enough.  

Here you are a photography of the vertical control. Hope this helps.
The weigh of the puppet holds on the leather strip, so you have all the fingers free to manipulate the wires for arms (the wire is from coat hanger). The leg bar is detachable and it is to be used with the other hand