This adapter mates an AN8 male flare to a 5/16 female quick connect, the largest step in the group. It comes up most often on return-side plumbing, where the factory circuit uses 5/16 line but the aftermarket regulator or surge tank is fitted with AN8 ports and you would rather adapt than rebuild the whole return. It also suits cases where a single AN8 hose kit has been bought for the car and the return connection happens to be the smaller size. As with the other quick connect adapters, seat the coupling until the retainer clicks and tug-test it before running the pump.