Hey all, either reassure me I'm not an idiot, or crush my delusions of competence and explain to me how this Silca pump chuck works on a Presta valve.

The brass tip threads beautifully on to a Schrader valve, but it's much too wide for a Presta, there's no seal. I bought it off eBay and the seller listed it as Presta compatible, but there's no way I can figure to make this pump fill a tube with a Presta valve. And yes, I've reversed the plastic insert and tried it both ways.

My thoughts are that this is a Schrader chuck or the seller failed to include the leather washer. Worst case scenario I'm just kind of dumb.