Angle Union for Cast Iron Rad Connection?

Somebody told me I need "angle unions" to connect some old cast iron radiators to conventional fittings on a 3/4-inch hydronic system. In the past, I've simply removed the original fitting and plumbed into the standard bushings on old rads, but it would sure be easier this time around to use what's already there.'



So, is that what I need and if so, where would I get some?



<img src="http://nefpexpo.net/signpics/radfitting1.jpg" alt="" />



I'm assuming it looks something like this:



<img src="http://nefpexpo.net/signpics/radfitting3.jpg" alt="" />