Bicycle Mechanics - Reassembling an old Shimano 105 rear derailleur

Oops.. I did a stupid. Took apart an old derailleur to clean it. When I went to put it back together I noticed that the cogs are not quite the same: one has a slightly larger flange. Which position does this go on? Closer to the derailleur body or farther away?

Thanks.

Oops.. I did a stupid. Took apart an old derailleur to clean it. When I went to put it back together I noticed that the cogs are not quite the same: one has a slightly larger flange. Which position does this go on? Closer to the derailleur body or farther away?

Thanks.

The Shimano-Europe site has lots of exploded diagrams of different parts. It's usually the newer parts, so you many not be able to find your derailleur, but it can help. Here's one for a slightly older 105 derailleur:
http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/RD/EV-RD-5500-1736_v1_m56577569830609118.pdf

By "cogs", do you mean "derailleur pulleys"? They're usually the same size. Only rarely are they different- and usually the bigger one goes on the bottom or farther away from the derailleur body.

Yeah, I mean the pulleys. I just never learned the real names for a lot of these things. This is an older 105, the pulleys just say "narrow" on them. But 1 has a slightly different, wider body. It is not actually bigger in diameter. I don't know if it even makes a difference, but I'd rather put it back together only once.

I'd still appreciate any advice on this if anyone knows for sure.

The one with a more squarish profile is called a guide pulley. It has a slight amount of side-to-side play and goes on top - closest to the freewheel/cassette cogs.
The other one is called a tension pulley. It has no side-to-side play and goes on the bottom.