I had bought a European Style Pen w/Roller Clip kit from Woodcraft.com and bought the bushings to match. Well, it has four bushings. Looks like two end bushings for the cap and nib and then a reducing bushing and what appears to be a center band sizing bushing. After studying the bushing set for a while this is what I've come up with.
The biggest end bushing is for the cap or finial. The smaller bushing is for the nib. The reducing bushing has the smallest end facing the nib bushing with the larger end facing the cap and the center band bushing aslo facing the cap end. I guess I turn the top half down to the center band bushing and then remove the bushing to make the tenon down to the reducing bushing. I'm calling it a reducing bushing because it steps down to a smaller diameter. So, have I got this right?
Here's a drawing of the above:

This is probably gonna be a my first pen since I'm still waiting on my order to come in from PSI!
Thanks,
Steve