Another coilover question thread, threaded collars for Koni / Bilstein, same size? Options

[PlaysWithCars]

Sorry if this has been covered already, but all of the searching and reading I've done has only led to confusion.

I bought a set of new threaded collars as part of a package with new Koni sport shocks. The collars didn't fit as tight as I would have expected so I pulled out a spare set of Bilstein shocks to see it they fit them any better (I recalled reading that Koni and Bilstein required different sized collars and thought I may have gotten the wrong ones). Anyway, they fit the Bilsteins about the same. So, out came the calipers and the shock bodies are essentially the same diameter: Bilstein - 1.973" / Koni - 1.978". I also measured two other shock sets and got the same results. So, I'm concluding the shock bodies are essentially the same. (IMG:style_emoticons/default/confused24.gif)

I found this post in the forum (http://www.914world.com/bbs2/index.php?sho...amp;hl=coilover) that talked about using an adapter from Coleman Racing and this one from JP where he used a plastic "shim" to get his fitting correctly (http://www.914world.com/bbs2/index.php?sho...amp;hl=coilover). Is this just nature of the beast that they don't fit tightly and need to have a adapter or shim installed? Is it the same story regardless of shock manufacturer?

Any guidance would be appreciated.