Its the square or rounded looking thing that goes between the cross guard and the blade. It stops rain from getting in side the scabbard. I think they also call it a chappe (don't quote me on the spelling of that).
The scabbard are not really like a glove there has to be room for movement in side so the blade can quickly be taken out. The rain guard is the only point where there is a glove like fitting between the two. It had to stop the rain from getting in but not stop the person from getting it out.
Swords cost crap loads even back when they where used you wouldn't want it to rust.
http://en.wikipedia.org/wiki/File:Sword_parts.svg
Link I use for my sword designs
I'll add something later on.
