I've never seen any 5/16 hex driver devices before (except on the Schrade tool itself)
Only thing that comes to mind are some of those reversable screwdrivers. You know the kind, right? They have a double-ended phillips on one end. You pull it out, flip it around, and there's a double-ended flathead on the other. I don't have one myself, but they're quite common. Anyhow, might the size on those double-ended bits be 5/16" hex??