Washing Machine / Dishwasher Y

Hey, Installing a new Zanussi dishwasher at home so I picked up a plastic Y in heatmerchants. The washing machine hose tightens home nicely but the dishwasher hose won't tighten, its as if the diameter of the nut is slightly too big and it just clicks as if its going to ring off.

These hoses are standard surely? Should I use some ptfe tape or pick up a metal Y?

Thanks lads