Looks like a good old Sedis chain. A KMC 8/9 speed chain will be a good replacement. Why did you change from an 8spd to a 7? You need a chain pin tool to remove the old chain and 'cut' the new chain to the correct size.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk