Originally Posted by
davidad
Any 6, 7, or 8 speed chain will work. I would get the KMC with a masterlink.
+1, except that older 6s chains were slightly wider than today's 7s & 8s chains. Anyway, it's simple math, your 21 speed bike has triple chainrings and 7 speeds on the wheel, so it's 3x7. Years ago we referred to bikes by the total number of speeds as you do, but for chain purposes you only care about the rear sprockets so you have a 7 speed and would buy any chain compatible that.