Originally Posted by Kontact

You can probably get any chain up to 11 to work on a 6 speed freewheel because they all have the same inner (cog) width. The only limitation is if the cogs are so far apart that the chain won't cleanly land on one cog or another - but 11 speed chains aren't narrow enough to wedge between the 3.5 space from cog to cog on 6 speed. So no chain is "rated" so much as SRAM doesn't bother making dedicated 6 speed chains for the repair market, since they don't need to. In poorer markets they do make 5/6 speed chains with an outer pin width approaching 8mm, which will not work on 7 speed.

There's plenty of old 5/6 speed chains NOS in boxes, which is why I advised the OP to use a narrower chain if there is a problem with FD rub. However, I used a SRAM Red Ti 10 speed FD as a friction 8 speed derailleur, and it is more than wide enough.