Having purchased and used the Avenger Extension Arm with 1-1/8 Swivel Spigot, I can tell you it's a great product.
That swivel spigot is fantastic for fine and easy articulations (the envy of many video and photo friends).
This extension arm will only fit on a standard light stand if you have a clamp. That means a standard light stand will not work by itself. You'll need the connecting clamp that sits on top of the light stand. The clamp will grip the extension arm. I'd buy the stand as well or maybe an Avenger super clamp grip head to go on your own light stand. Two options for grip heads to hold your extension arm are below:
GOOD (also versatile for other uses)
Also, I'd be careful if you use a standard light stand with something to clamp this extension arm. The extension arm is heavy, and for good reason (i.e. quality). You'll need a heavier light stand or at least a sandbag to hold a light stand that equips this extension arm.
I hope this helps you in your purchase. I'm a careful shopper myself, so I value solid information up front.