For one modern car, a metric combination set spanning roughly 8 mm to 19 mm covers most of the work a wrench does, and ratcheting wrenches are a convenience upgrade rather than a starter purchase. Wrenches are the tool you reach for when a socket cannot get on the fastener or when you need to hold a nut while turning a bolt. That is a narrower job than the size of the wall display suggests.
The two things worth spending on are not in most beginner sets at all, and they come at the end of this page.
What a Combination Wrench Actually Is
One wrench, two ends, the same size on both.
The box end is the closed ring. It surrounds the fastener and contacts it on multiple faces, so it grips well and is far less likely to damage the head.
The open end is the U-shaped jaw. It slides onto a fastener from the side, which is its whole reason for existing, because sometimes there is no way to get a closed ring on.
The rule that follows is simple and most people ignore it: use the box end unless you physically cannot. An open end contacts only two faces of the fastener and applies force in a way that tries to spread its own jaws apart. That is the mechanism behind a large share of rounded nuts in home garages. Open ends are for access and for holding, not for breaking things loose.
Most box ends are twelve-point rather than six-point, and there is a good reason for it: a wrench cannot reposition itself the way a ratchet can, so twelve engagement positions instead of six is a serious practical gain. The trade involved is set out in the comparison of six-point and twelve-point tools.
The Sizes You Will Use, and the Ones Sets Skip
Look at what manufacturers put in their smaller metric sets and a pattern appears. A typical eight-piece metric set runs 8, 10, 12, 13, 14, 15, 17 and 19 mm. Larger sets fill in from roughly 6 mm at the bottom to the low 20s at the top.
Notice what gets skipped: 9, 11, 16 and 18 mm. That is not because those fasteners do not exist. It is a manufacturer's judgment about which sizes appear often enough to justify the piece. Your car has whatever sizes its designers chose.
Two practical conclusions.
If a job stops because you are missing an odd size, buying that single wrench is almost always better value than buying a bigger set to obtain it.
And before buying anything, settle whether you need inch sizes at all. On a modern car you very likely do not, and a combined metric and inch set doubles the drawer for a second half you may open twice a year. That decision is worked through in metric versus SAE sets.
Ratcheting Wrenches: What You Are Paying For
A ratcheting box end lets you turn a fastener without lifting the wrench off between strokes. On a long bolt in a place your hand barely reaches, that is a genuine time saving and a genuine frustration saving.
What you give up is real too.
Thickness and height. A ratcheting box end contains a mechanism, so it is bulkier than a solid ring. It fits fewer places. The wrench that reaches the fastener you cannot reach is often the plain one.
A mechanism that can fail. A solid box end is a piece of forged steel. A ratcheting one has moving parts, and those parts are the weak point. Makers publish torque ratings for their ratcheting wrenches, so check the maker's own figure rather than assuming the ratcheting wrench matches the solid one it sits next to in the set.
The working rule most people arrive at eventually: break the fastener loose with a solid box end, a socket or a breaker bar, then spin it out with the ratcheting wrench. Use the ratchet mechanism for speed, not for force.
The swing arc arithmetic is the same as it is for ratchets. The advertised arc is 360 divided by the tooth count, and the gains flatten quickly past about 72 teeth, which is covered in full in the piece on whether ratchet tooth count matters. A wrench adds its own constraint on top: the body still has to swing, so a fine arc in the mechanism does not help if the handle has nowhere to go.
The Two Types Most Sets Leave Out
Flare nut wrenches, also called line wrenches. These look like a box end with a slot cut in it. The slot lets the wrench pass over a tube, and the remaining ring grips the fitting on far more faces than an open end can. They exist because hydraulic line fittings are relatively soft and an open-end wrench rounds them quickly.
There is an important stop attached to this one. Brake lines, fuel lines and the fittings on them are safety-critical, and this site does not describe that work. Brake hydraulics have to be reassembled to the manufacturer's specification and correctly bled, fuel lines are pressurized, and an error in either is discovered while driving. Own the wrench if you like, and take the job to a qualified mechanic.
Stubby wrenches. Short-handled versions of the same tool. They give up leverage in exchange for fitting into spaces a full-length wrench cannot enter. In a modern engine bay that trade is worth making more often than you would guess, and stubbies are cheap because they are small.
A flex-head ratcheting wrench sits between the two ideas and is genuinely useful, but it is a third purchase, not a first.
What to Skip
A giant combined metric and inch set, unless you have already established you need both.
An adjustable wrench as a substitute for the right size. It contacts two faces, its jaws have play by design, and that play grows with age. It is the most reliable fastener-rounding device in most home garages. Keep one for plumbing fittings and emergencies, not for car work.
Duplicate sizes bought "in case". A second 13 mm is genuinely useful, because holding a nut while turning a bolt needs two tools. A third is decoration.
Very large sizes, at first. Fasteners above about 19 mm on a car are usually approached with a socket and a long handle rather than a wrench, and that is a drive-size decision rather than a wrench one, covered in what each socket drive size is for.
What Changes Between Tiers
Budget combination wrenches are broadly serviceable, and the honest failure points are consistent.
Fit tolerance is the main one. A loose jaw on an open end damages fasteners faster, and it gets worse as the tool wears.
Finish and markings. Cheap size markings disappear, which sounds trivial until you are sorting a set by eye under a car.
The ratcheting mechanism is where the tiers separate most, because it is the part with something to go wrong.
Warranty. A replacement policy that is actually honored is most of what you are paying for at the top tiers, and it matters more on tools you will own for decades than on tools you will use once.
Where This Stops
Wrenches loosen and tighten. They do not measure.
We publish no tightening figure for any fastener on any vehicle. Those numbers depend on the exact year, model, engine and fastener, and they belong in the manufacturer's service information for your vehicle. Brake, suspension, steering, airbag and fuel-system fasteners in particular must go back to specification, and a wrench cannot tell you when you have reached it. If you do not have the figure and a reliable way to reach it, that work belongs with a qualified mechanic.
FAQ
What size combination wrench set do I need for car repair?
For one modern car, a metric set spanning roughly 8 mm to 19 mm covers most wrench work. Buy odd sizes individually when a job asks for one, rather than buying a larger set to get a single wrench.
Are ratcheting wrenches worth it?
They are a convenience upgrade. They save real time on long fasteners in awkward places. They are thicker, so they fit fewer spots, and their mechanism is the weak point, so break fasteners loose with a solid tool and use the ratcheting end for speed.
Do I need both metric and SAE wrenches?
Usually not for a modern car. Inch sizes earn their place on older American vehicles, trailers, aftermarket brackets and shop equipment.
Why do wrench box ends have twelve points?
Because a wrench cannot reposition itself between strokes. Twelve engagement positions instead of six means half the repositioning in a tight space, which matters more on a wrench than it does on a ratchet.
What is a flare nut wrench for?
Hydraulic line fittings, such as brake and fuel lines. The slotted ring grips far more of the fitting than an open-end wrench, which rounds those soft fittings easily. The tool is worth owning, and brake and fuel line work itself belongs with a qualified mechanic.
The Short Version
- Metric, roughly 8 mm to 19 mm, covers most car wrench work on one modern vehicle.
- Use the box end unless you physically cannot. Open ends round fasteners.
- Sets skip 9, 11, 16 and 18 mm. Buy the odd size on its own when a job needs it.
- Ratcheting wrenches buy speed, not force. Break it loose with something solid.
- Flare nut wrenches and stubbies are the two most under-bought types, and brake and fuel line work still stops at the shop.
- The adjustable wrench is not a substitute. It is the most common cause of a rounded nut in a home garage.
