How does the flash attach securely to this eBay bracket?

I have that umbrella holder too and I don't use it. It does not hold the flash securely. It's only good for flashes with the twist lock. You'll have troubles getting it on a 580ex and vivitar 285hv but it'll work fine with a 430ex.

Instead, get this one instead:
http://www.dealextreme​.com/details.dx/sku.51​31

It has a silver knob on the side that allows you to adjust the width and tighten it.

I actually don't use any of those umbrella holders anymore. I use the photoflex umbrella holders with the stud. They cost twice as much ($20) but they hold the flash more secure.

dennytang wrote in post #6132552
I have that umbrella holder too and I don't use it. It does not hold the flash securely. It's only good for flashes with the twist lock. You'll have troubles getting it on a 580ex and vivitar 285hv but it'll work fine with a 430ex.

Instead, get this one instead:
http://www.dealextreme​.com/details.dx/sku.51​31

...snip.

Thats the exact one that turned up Dennytang - still need the adaptor and a bigger thumb screw for my hands, the screw is being made and the hotshoe adaptor is on order.

the 580 EX II has the weathersealed rubber guard at the back...so if you buy this... you probably wont be able to slide it up and down on the rail.

EDIT: looks like you already got it... sorry!

I recommend ALZO’s Flash Photo Umbrella Mounts. I have a small review here.

I replaced my cheap ebay once with these. Any time you tighten up ebay mount, they creek like they about to break... that scares me...