Picked up an old jumbo joe today for $8

[MeatAndPotatos]

I still don't understand why people put the wing-nuts on the outside … 

Nice score, BTW.  Great little cookers.

On the legs? Because the instructions say to...
http://www.manualslib.com/manual/783393/Weber-Jumbo-Joe.html?page=9#manual

Also helps keep the threads and wing nut out of the ashy-dirty part of the grill to allow easier disassembly if needed for travel. This way only the slot on the top of the screw gets gunked up and that is easier to clean then threads....

[MacEggs]

I still don't understand why people put the wing-nuts on the outside … 

Nice score, BTW.  Great little cookers.

On the legs? Because the instructions say to...
http://www.manualslib.com/manual/783393/Weber-Jumbo-Joe.html?page=9#manual

Also helps keep the threads and wing nut out of the ashy-dirty part of the grill to allow easier disassembly if needed for travel. This way only the slot on the top of the screw gets gunked up and that is easier to clean then threads....

Thank you for that.
However, the manual you link to is for the newer JJ.
Troy picked up an older one with a deeper bowl that is similar to a standard 18" kettle.
The wing-nuts help hold the charcoal grate in place, as I believe is the same for a 14" SJG.

When I rescued an Outrider (SJP), I had no instructions to go by, so I have the wing-nuts on the inside.  YMMV

According to the following schematic, the wing-nuts go on the inside.

http://help.weber.com/schematics/browse.aspx?all=1&model=51004

[MeatAndPotatos]

Ahhh, didn't know they were used to hold the charcoal grate in place. Makes sense then.

In general I usually look to keep the threads both in the cleaner area of whatever I am working on, and on the more accessible side of what I am working on.... Though thats really just whenever there is no function to them being one way or the other.