Uhh well if 1/8" is for each wire, then you'd probably need a pretty huge piece of heatshink! I'm not sure, probably be a good idea to go to a hardware store and "eyeball" it
What style of heatshrinking are you trying to do? are you trying to cover individual wires? are you trying to just neaten off the transition between sleeving and bare wires or are you trying to sleeve the whole bundle as it enters the connector?