The lower section of the Wall St 2/3 and it's similars (Sierras and a few others, but not all that look like that are put together the same) is basically a short tube with a nib inserted into it, a black enameled metal tapered "sleeve" and a centerband that has the tube pressed into the inside and the outside matches the inner diameter of the tapered sleeve. The inside of the top of the centerband is threaded for the transmission, and the outside is sized for the brass tube, but small enough that it slides, which provides the twist action.
To customize the centerband effectively and easily, I would turn away the existing visible part of the centerband, without harming the other parts of it, and glue another material over the turned down part, then turn that to match the original sizing.
Another option would be to replace the black tapered sleeve with something also. The difficulty comes in dealing with the nib and tube that are inside the lower section. They are close to 7mm, but NOT 7mm. You CANNOT use a standard 7mm nib with that tube, plus it has a small ridge to hold the tapered sleeve that is not on any other nib I have seen. Standard 7mm tubes will not press into the centerband and hold either, and the length of the entire section is critical to the extension/retraction of the refill. There is also some "slop" to the nib/tube/centerband fit that is controlled by the tapered sleeve (i.e. without the sleeve, it is possible to press the tube too far into the centerband, making it too short and the refill will not retract fully, DAMHIKT...:wink
so measuring length closely is critical, and you need to leave material beyond the lower tube, so that the ridge that originally fit in the lower tapered sleeve will fit inside.
I did a few of these where I replaced EVERYTHING except the nib and upper trim piece (One is
here, the other I think was entered in last year's BASH, but I didn't find it at the moment...). I keep meaning to put together a how-to on doing this, but haven't gotten around to it yet...
