mounting a satellite onto stairway railing

Hey need some ideas on how to do this. After finally deciding to keep my sonus faber concertino's as surrounds I need to mount one of them on my steel stairway railing to put it out of the way.

I was wondering if anyone has any easy solution for some kind of clamp that would attach to a vertical steel bar and also attach to a platform which I can put my speaker on.

Ideally I would like the platform to be able to have some holes in the bottom so I can screw and secure the speaker by the holes preplaced in the bottom of the speaker.

We in the film business would suggest what is called a Mafer Clamp. It is designed to clamp onto something just like that. Add a Spud adapter and you can mount anything to it. Look at this:
Google "mafer clamp" and you'll find other stuff as well. Look for Matthews Studio Equipment also. Good luck.
great idea. looks like with the selection of clamps i'll be able to find something that'll work well

follow up question. is there a standard size bolt for the threads in the bottom of my speaker? wondering what I need to buy.
Being Italian made speakers, my guess would be that they are "metric" machine bolts. I have a pair of SF Walls but they have two wood screws on the back for mounting. Concertino's are small and light enough that you could take them to the hardware store and find the right bolt, or you could also try contacting Sumiko at 510-843-4500 (Berkeley California) and see if they can tell you the thread size. Good luck.
Any wall mount bracket shaped like a J or L would work. You can just use 49cent metal hose clamps to mount the bracket to the railing. Hose clamps are quite strong and don't loosen.

I wouldn't do this at all though. The speaker will resonate through the railing as well as vibrate. If the speaker isn't mounted to the shelf with screws, odds are it will fall off.

If it is mounted securely, it will vibrate like mad...
I would either hang it from the ceiling, use a speaker stand or put it somewhere else that is more "stable".