Matt, the Ronnie is a rear rim, and the Reggie is the front version (basically a scaled down Ronnie).
You can, of course, run a Ronnie on the front if you like, but theyre a bit hefty! (And you'd have to run a 19" tyre if you have a mod bike).
Reggie
Ronnie
Look similar, but different widths and weights.
Hope thats of use,
Adam