Question

open - end wrenches
an open - end wrench is identified by its \open ends\. the ends grip a bolt or nut on two faces (or flats). when force is applied to the wrench, contact is made with only two faces (flats), thus less force is transferable to the bolt or nut, compared to a box - end wrench that grips on all faces.
because of its open ends, the wrench can fit onto the bolt or nut from the side, making the open - end useful in situations where space is limited.
the open - end wrench has different sizes on each end. the open - end wrench head is usually at a 15° angle to the handle, enabling an extra 15° of movement when the wrench is turned around on its axis. open - end wrench sizes vary. special tools can be designed using an open - end, providing access to objects that are otherwise difficult if not impossible to reach with a box - end wrench or socket.
why does an open - end wrench transfer less force than a box - end wrench?
open - end wrenches are made of soft, non - hardened steel alloy.
open - end wrenches are notably shorter than box - end wrenches.
an open - end wrench only grips two faces (flats).

Explanation:

The text states that an open - end wrench grips a bolt or nut on two faces (flats), while a box - end wrench grips on all faces. Less surface contact means less force can be transferred.

Answer:

An open - end wrench only grips two faces (flats).