MSR Pump Plungers: There are four types of replacement plunger - it is important to get the correct one as they are not interchangeable. They are:
Duraseal: The new pump introduced in 2004 (418809 unpackaged and 318638 packaged and more expensive!).
Flanged: This was standard from 2002 - 2003 (318638F) - originally this had a leather washer but now has a rubber one. It fits all old (non-Duraseal) pumps that are grey in colour.
Original: This fitted all stoves made prior to 2002. It had no flanges but did have a collar and was red in colour. Sorry - no longer available.
Really Old Original: This was as per the Original but has no collar (ie you need to have not lost the two part collar) and fitted all stoves made prior to 2002. It was black in colour. Sorry - no longer available.