These double open-end wrenches have a head at each end that grips and turns SAE (inch) fasteners of a specific size.
They allow access to fasteners from the top and side compared to box wrenches that can only access a fastener from the top.
Wrenches with two head sizes have a different size on each end to fit a different-sized fastener. Wrenches with two opening angles have a different head angle on each end that provides clearance around obstacles.