Drawer runner fitted beneath drawer

Can someone give me a heads up for a runner that will fit entirely below a drawer, the drawer (or pullout) will sit on top of the whole thing. As far as I can tell most of the ones described as "bottom mounted" merely have a bracket that the drawer sits on while the runner is conventionally fitted to the side of the unit.

If there is a blindingly obvious answer to this, my only defence is ignorance.

Thanks.