The second proper tool for removing and attaching nuts and bolts is the wrench, and compared with the ratchet and socket system it’s simple—a standard wrench has zero moving parts. Much like a socket, each wrench is sized to fit a specific nut or bolt, and can be had in SAE or metric sizes (or, if you have a British car or motorcycle from the 50s or 60s, the rapidly vanishing Whitworth system).
The working end of a wrench can be of two basic styles. A box-end wrench has an enclosed circular shape, and must be dropped over the top of the nut or bolt. An open-end wrench is self-descriptive: It’s open and designed to slide on the nut from the side.
The box-end wrench works better on very tight and/or damaged fasteners, since it grips all six sides. It’s also less likely to slip off than an open-end wrench. Note that, in contrast to the sockets discussed earlier, the vast majority of box-end wrenches are 12-point rather than six point. The reason is that, in contrast to a ratchet and socket, you have to lift the tool off the fastener each time you turn it. With a six-point wrench this would require a full 60-degree turn—cumbersome at best and impossible in many spots. A 12-point end only requires 30 degrees of turn. Just as with sockets, Snap-on’s Flank Drive system or a copy thereof has become common on all but the cheapest wrenches.
An open-end wrench can slip on a fastener from the side. This is an obvious advantage when there is restricted access from above, or if you need to remove a flare nut on a fuel or oil line where it would be impossible to use a box-end wrench or a socket. (Dedicated flare-nut wrenches have what looks like a box end with one section missing; this allows the end to slip over the fuel or oil line, yet grip the nut on five of its six sides. This helps prevent crushing soft brass flare nuts.) Since an open-end wrench only bears on two sides of the fastener, the potential for rounding off a stuck one is higher. Also, since the open end lacks the inherent rigidity of a box end, the two ears need to be comparatively massive to maintain sufficient strength, and this can limit where the wrench will fit. Finally, an open end wrench must be turned a full 60 degrees to engage the next flat on the fastener, although since most open-end wrenches are offset by about 15 degrees you can cheat this a bit by flipping the wrench over between turns.
Looking at the simplicity of an open-end wrench, you might imagine it would be difficult to improve. However, once again the clever engineers at Snap-on thought outside the box: Their Flank Drive Plus system incorporates a series of grooves and a chamfer in the flats of the wrench jaw, ebabling it to grip the sides of a fastener much more agressively than smooth jaws. As with the earlier Flank Drive for sockets and box-end wrenches, many other companies now produce a similar system. One thing to note is that this modification will mar the surface of the fastener if enough force is applied—no doubt the reason Snap-on also still sells wrenches without Flank Drive Plus.
You could save some space, weight, and cost in your tool kit by buying wrenches that are either all box end or all open end, and which incorporate a different size at each end—14mm and 15mm, 16mm and 17mm, etc. However, because of the mix of advantages and disadvantages of each style discussed earlier, I prefer to accept the extra expense, weight, and bulk, and carry combination wrenches that have one open and one box end of the same size. It happens very frequently when working on a vehicle that one or the other will be the best to use, and it’s nice to have them right there in one tool.
A double box-end wrench (17mm and 19mm) above; a combination wrench (19mm) below.
Other ‘improvements’ you’ll see on this tool might be of less value. Wrenches that incorporate a ratcheting box end are becoming more and more common, and the theoretical advantages to the concept are obvious. The downside, however, is a big one: The head is much bulkier than that in a non-ratcheting head. Since one of the salient advantages of a standard box end is its small diameter, able to fit in very restricted spaces, this pretty much eliminates ratcheting heads from consideration for my traveling tool box. I’ve also tried a couple of ratcheting open-end wrenches, which employ a sliding pawl that moves out of the way in one direction and locks in the other. So far I’ve not found one that felt both smooth and precise, i.e. close-fitting to the fastener. The head, as with the ratcheting box-end counterpart, is bulky, and has to be fully engaged on the fastener to operate—thus those cramped situations where you can just get the wrench over part of the nut will defeat the mechanism. So I’ll maintain my trust in standard open-end wrenches–especially for field use, when simple, pure function is paramount.
Kobalt ratcheting box-end wrenches.
Kobalt ratcheting open-end wrench. Note that both these photos were pirated at a local Lowe's because I have no intention of buying the tools.
What to look for? I like fully polished wrenches, which are far easier to keep clean than those with a blasted finish. If you compare a cheap wrench with a good one you’ll find that the good one, with better steel, will be less bulky, especially around the box end, where less material is needed to maintain strength. This can mean the difference between the tool fitting or not fitting over a fastener close to an obstruction.
A fully polished wrench (above) is easier to keep clean than one with a blasted finish.
With that said, however—while I have broken many cheap sockets, I cannot remember ever breaking a wrench. Therefore, while the Gold Standard wrenches are a delight to use, there are many fine alternatives available at fractional pricing. I’m especially impressed with the American-made Wright wrenches, which are available fully polished and with a Flank-Drive-Plus-type open end called Wright Drive. An excellent source for these (and many other U.S.-produced tools) is the Harry Epstein company (here), in business in Kansas City, Missouri, since 1933. The Craftsman Professional line is still decent, although I’m not fond of their gimmicky ‘Cross-Force’ offset-head version. Their conventional 24-piece fully polished metric combination wrench set is less than $50. Other good brands include SK, Proto, Cornwell, and the Home Depot and Lowe’s house brands. Stanley offers an 11-piece set that is a bargain at around $25, although it stops at 17mm and you really should have a 19 in your kit.
On that note: A comprehensive set should include wrenches from about 6mm (or 1/4”) up to 19mm (3/4”). You can go up to 25mm (1”) or so, but beyond that wrenches begin to get very bulky and heavy (not to mention expensive) for the single size fastener they’ll fit. Unless you have a specific application on your vehicle that requires a wrench, I’d stick with sockets for larger sizes.
A 32mm wrench is getting pretty bulky.
A 19mm wrench compared to the 32mm. For most needs the 32mm socket will suffice.
Finally, I like to store my field wrenches in a roll to keep them organized, quiet, and scratch-free. Unfortunately 95 precent of the wrench rolls on the market simply don’t hold enough wrenches. Nine or ten pockets is standard; a few hold a dozen, yet a full set of metric wrenches from 6mm to 24mm—even if you skip the rarely used 20 and 22mm—adds up to 17. A few years ago I snagged a giant Snap-on-branded roll on Ebay, with no fewer than 21 pockets and a generous extra flap of material that made a superb place to keep other tools out of the dirt. (See the opening photo of Tools 101, part 1.) I just discovered that that Snap-on roll was probably this one with the fancy brand added on so Snap-on could charge double.