Three styles, two kinds of grip
Fixed-size wrenches come in three basic styles. An open-end wrench has a U-shaped opening that slides over a fastener. A box-end wrench has a closed loop that surrounds it. A combination wrench is a hybrid with an open end on one side and a box end on the other, both sized the same. The differences come down to how many points of contact the wrench has with the fastener and how it can get to it.
Open-end wrenches
An open-end wrench slips onto a nut or bolt from the side, which makes it useful where there is no room to lower a closed tool straight down over the head. It is also what you need on a nut that sits partway along a long bolt or on a pipe fitting, where a closed loop would have to slide over a long threaded end.
The trade-off is grip. An open jaw usually contacts only two flats of the hex. Under heavy force, the jaws can spread slightly or slip, and that contact can round the corners of the fastener. Many open-end wrenches have the jaw angled about 15 degrees off the handle. That small angle means you can flip the wrench over to get a new bite when swing room is limited, working in short arcs.
Open-end wrenches are best for light to moderate turning force, for starting or finishing a nut that is already loose, and for places where nothing else fits.
Box-end wrenches
A box-end wrench wraps around the head and grips at the corners. Because the force is spread over more of the fastener, a box end generally resists slipping better and is gentler on rounded or worn heads than an open end. For tight or stubborn fasteners, it is the better of the two choices, and it is generally preferred for final loosening and tightening when you can reach the head from above.
Box ends are usually either six-point or twelve-point, a distinction that affects grip and access. A twelve-point opening can engage the fastener at more angles, which is handy in cramped spots, while a six-point one holds the flats more fully. The same trade-offs apply to six-point sockets, which is a reminder that the wrench versus socket question is often about access more than strength.
Box-end wrenches often have an offset between the loop and the handle, which lifts the handle above surrounding parts and gives knuckle clearance. Some have a deeper offset to clear a long threaded stud.
Combination wrenches
A combination wrench puts both ends on one tool in the same size. That makes it a practical standard for a general set: you can start a stubborn fastener with the box end, then switch to the open end to spin it off in a tight area, all with one wrench. If you buy a single set to begin with, this is the style most often chosen, and a good range of sizes in both inch and metric covers most basic work. Whether you need both systems depends on what you work on, and it is worth reading about metric versus SAE sizing before you buy.
A variation is the ratcheting combination wrench, whose box end contains a small ratcheting mechanism so you do not have to lift and reposition the tool after each swing. These are convenient in tight spaces but their small mechanisms may be less strong than a solid box end, so for the final stubborn break-loose a solid wrench or breaker bar is often more suitable.
Choosing between them
| Situation | Often the better choice |
|---|---|
| Tight, stubborn or rusty fastener | Box end |
| Nut on a long bolt or a fitting on a line | Open end |
| Little room to swing | Open end or ratcheting box end |
| Light, quick adjustment | Open end |
| Final tightening to a spec | Torque wrench with a socket |
| Rounded or worn head | Six-point socket or box end |
Fit and size
A wrench should fit snugly with little wobble. A loose fit rounds corners, and that is the most common reason a good bolt becomes a bad one. If a wrench rocks on the head, try a different size or system rather than forcing it. Keep the wrench fully seated on the head, not just on the edge. For open ends, make sure the jaw reaches the full depth of the fastener.
Never add a pipe to the handle for extra leverage unless the tool is designed for it, and do not strike a wrench with a hammer unless it is marked as a striking tool. Both habits can damage the wrench or send it flying.
Pulling, not pushing
A reliable habit is to pull the wrench toward you rather than pushing it away. If the wrench slips or the fastener lets go, your hand moves away from the work instead of into it. When you have to push, use the open palm. Wear eye protection when working with stubborn fasteners, since rust and grime can fall off. If a fastener won’t move with reasonable effort, penetrating oil and patience tend to be better than more force.
Care
Wipe wrenches clean after use, especially after contact with oil, brake fluid or solvents. Dry them before storage to prevent rust. Look over the jaws and loops for cracks, spread, or worn corners, and retire any tool that has them. A spread jaw won’t grip, and a cracked one can break. A set kept in a roll or rail stays organized and shows at a glance when one size is missing.