step 2. Using the longer bushing #PKGEMBU, place the 2 black serrated bands (in the kit) over the narrow end of the bushings to use as 4mm spacing (see Diagram E). I did not get that bushing nor is it illustrated in Diagram E Assembly.
Will call tech help tomorrow, and ask if they have different instructions or illustration showing how or why you need #PKGEMBU. The bushing set ordered for this kit is #PKPOLBU-6
If your talking about the Brass Sizing Tube, am following instructions. Putting those two black serrated bands on that tube not going to accomplish much. Once you install the mechanism nut you throw away that brass sizing tube and install the connector. If you press the mechanism nut beyond 18.5mm may have trouble screwing on the pen click mechanism. Not sure the pen will work.
Once you install the connector, you screw in the click mechanism, doesn't matter if you install refill, spring, and tip next or install, plunger spring screw on plunger & cap/clip assembly next. It's easier to screw on plunger before screwing on cap assembly. Steps in the instructions out of order.
JMHO, installing the mechanism nut 1st, before the tip nut much easier. Less chance of damaging the tip nut, trying to install mechanism nut.