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The title says it all.

The flip side of the question is whether a metric wrench set is sufficient for cars from European/Japanese/Korean makers (but, of course, I can't ask that question here lest I break the one-question per post rule :^).

  • If I understand the question right, you would like to know what kind of wrench you need for GM? Imperial or metric? I don't think there is a difference. I mean if we germans have a 12 mm key, you have your silly 3/4 inch key or what ever.The point is, metric or imperial, the size is the same. – Watsche Jul 29 '14 at 14:03
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    @watsche In my experience there is a perceptible difference in feel. A wrench at the exact size needed will fit with pressure points throughout the bolt. An imperial wrench used on a metric bolt will work, but it will torque at two thin lines at two edges of the bolt. If a lot of force is needed, one can strip the bolt. – Calaf Jul 29 '14 at 17:22
  • For many years , I have found both Metric and English sockets are necessary ( GM and Nissan ). – blacksmith37 Mar 5 '18 at 15:43
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To directly answer your question: GM cars are primarily (if not entirely) Metric these days (probably since the mid-to-late 90's). The Korean/Japanese/European cars are all going to be Metric as well.

You should be able to get a small ratchet set which contains both SAE and Metric sockets in it. If you are serious about outfitting your car, you'll also want to get a set of wrenches (spanners) in both Metric and SAE, a set of screw drivers (a couple different sizes/lengths of flat and Philips), a pair of slip joint pliers, and maybe an adjustable wrench. All of these can be purchased through various means (online/in-store), but are very easy to obtain. Don't go spending a ton of money on tools. Here in the States (not knowing where you live), you can purchase these at any Sears, Lowe's, Home Depot, or even Harbor Freight for a relatively low price. All of these stores offer lifetime warranties on their tools, so replacement upon breakage is guaranteed.

With that said ... it may make you feel better to have a set of tools in your vehicle, by all means get them. In most cases though, today's modern cars are going to be giving you hints that something is going wrong with the vehicle, such as a trouble light. In this case, you'll more than likely be able to safely drive it to a shop or home to get things sorted. Usually if it breaks down, there is nothing you are going to be able to do with it on the side of the road, so having the tools with you is not going to do you much good. About the only tools I take with me is a good set of jumper cables and a cell phone. I've used the jumpers many times to help other people with their dead batteries. Beyond that, the cell phone is for the occasions when I am broke down, which doesn't happen very often, but can happen to anyone. Other than that, I like to text and drive ... J/K.

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If I were going on a long road trip in my Opel (which is a GM brand), I always take at least the following along:

  1. 2x Adjustable wrenches. One big and one small. Saves space and can fit any size nut.
  2. a set of allen keys. They're used to undo things like your seats, some engine components, etc.
  3. a set of torx keys. They're like allen keys but with star heads. Same as with allen keys, but on some cars you need a torx key to undo your dashboard or instrument cluster.
  4. a very sharp knife. For cutting, obviously.
  5. a bottle of water. For the radiator or for when you need to wait 8 hours for help.
  6. 6 feet/2 meters of radiator hose. To replace a burst hose. You can use radiator hoses for non-radiator duty, but you can't use non-radiator hoses for radiator duty.
  7. a couple of bungie chords. For tying stuff down, not jumping off bridges.
  8. wheel spanner. For spannering a wheel ;)
  9. jack.
  10. a set of screwdrivers.

For short trips I can forego the water bottle, radiator hose and bungie chords.

And you may also want to drive around with a couple of spare bulbs. They cost less than a candybar per set and could save you lots of money in fines. If you're paranoid like me, you may even want to have set of replacement headlight bulbs. They're a bit expensive, but not nearly as expensive as a couple of nights in hospital.

And for the cool factor, you can get yourself a bluetooth OBD2 adapter and an app like Torque Pro for android (there is something similar for Windows Phone 8 and iOS devices) which will allow you to see any fault codes reported by your car's onboard diagnostics system. Anytime your Check Engine Light goes on, the app can be used to identify what the problem is.

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    The hint to the bluetooth OBD2 adapter is invaluable. – Calaf Jul 15 '15 at 16:20
  • + wire cutter, duct tape ( temporary repair of hoses) , electric tape , Metric and English socket sets, variety of wires and hose clamps ; should pretty much handle emergencies . I prefer an empty container to a water bottle because if water is needed it is likely gallons. I did save myself with a propane bottle in nowhere Wyoming once, but that is too much stuff to routinely carry. – blacksmith37 Mar 5 '18 at 15:40
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I carry two ratchet sets, one in 1/4" drive and the other 3/8" drive with a good amount of overlap between the two, all in the same tool box. For many GM vehicles, you're going to need both metric and SAE (aka Imperial or Standard). Metric is rapidly displacing SAE but the evil devils continue to use a few SAE here and there. Just the socket sets alone won't be sufficient. All the sockets in my sets, with a couple special exceptions, are 6-point as they're more positive at driving hex head bolts and nuts. Unless you're working on aircraft that use 12-point fasteners, you shouldn't need 12-point.

  • SAE sockets should handle 1/4" up through 3/4", including 5/32", 7/32", 9/32" and 11/32".
  • Metric should cover 4mm through 19mm, including a 5.5mm, and a 4.5mm if you want to be truly comprehensive.
  • Add 2" and 6" extensions, U-joint swivels and breaker bars for both drive sizes. The breaker bar its most important for the 3/8" drive. Adapters to go from 1/4" drive to 3/8" sockets and from 3/8" drive to 1/4" sockets come in handy, allowing any socket to be used with any ratchet drive.
  • GM is using 19mm lug bolts now and their torque will be too much for a 3/8" drive. The lug wrench with the spare tire will handle the 100 ft-lb torque spec lug bolts.
  • Put in a "spinner", aka "driver handle" for the 1/4" drive set which allow you to use its sockets like a nut driver set. Good ones have the shaft extending completely through the handle with a 1/4" drive socket on the end of the handle in which you can use the ratchet or breaker bar for additional torque.
  • You will need tamper-proof Torx (with the hole in the middle) and metric hex (aka Allen) wrenches; You can get these as sockets for the 1/4" drive and use the spinner handle with them, but a more compact method is a 1/4" hex driver handle and a set of this stuff in 1/4" hex bits. Include #1, #2 and #3 Phillips, and the equivalent size flat tip screw driver bits. You'll need the #3 Phillips for things like license plate screws. They sell sets of tamper proof bits in
    1/4" hex drive in very compact boxes that also include the Phillips and flat tip bits.
  • Two adjustable (aka crescent) wrenches, a 6" or 8" and a larger 10" or 12" can give you an extra wrench to put onto the other end of a fastener to hold it in place while you tighten it with one of the ratchet wrenches. Much less space consumed than two tool rolls of combination wrenches in SAE and metric. Take care when using the adjustable wrenches as they're not called nut lathes and bolt rounders for naught; use the ratchet sets whenever possible.
  • Two pliers, one standard slip joint and the other needle nose with wire cutter down near the hinge pin can help grip stuff and retrieve stuff, and for additional retrieval capability add a magnetic screw retrieval wand. About the diameter of a large screwdriver shaft with a strong magnet at one end.
  • Nylon head mallet with a 2-3" diameter head and a 2-lb ball peen hammer. Shouldn't be beating on any fasteners or tools with a hammer, but it can be useful for nudging something back into place. The mallet will help keep you from marring things you don't want marred by a metal hammer.
  • Electrical tape in the event you need to splice a couple wires together, plus a small roll of #16 copper stranded wire. The needle nose are the wire cutters and with some care (and practice) can be used as wire strippers. Color doesn't matter in an emergency. UV resistant Zip ties, in assorted lengths, in UV resistant black can tie wire bundles back together and help route wiring. Augment this with a small multimeter that can check voltages and look for shorts and opens. I have an old Triplett Model 310-C that was my father's. They've been around for eons, Triplett still makes them and they're quite compact. Downside is it's an analog meter, which you do not want to drop. The case is nearly bulletproof but an analog meter movement with a needle on jeweled bearings might not emerge unscathed. If you're not accustomed to analog meters with needles, get a digital with a fairly hardy and durable case, but you don't need to break the bank on a Fluke for the car trunk.
  • Fuse assortment that includes the sizes and amperage used by your car, with several of each. I used to carry extra bulbs but don't any more. Bulbs have become extremely long life and very reliable. I think the only bulbs I've used in the past fifteen years are a few small #194, two for the rear license plate lights and one for a rear tail light side marker (not the main bulb). Had an extra #194 left over from the side marker replacement and tossed it in with the fuses. Been eons since I've had a headlamp, tail lamp or turn signal lamp burn out.

All this can fit in a smaller tool box than you might think, particularly a metal one. Ditch the blow molded boxes the ratchet sets will probably come in as they're massive space wasters. Put sockets onto socket strips; the metal kind can cut your fingers. They make heavy plastic ones that work just as well. With modern vehicles made since about 2000, if there's something beyond this tool set, you will need a garage.

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Depends entirely on the vehicle and how you drive it. If the vehicle is reasonably recent, and not all beat up, and you don't beat it up, then the tool you may need MOST for emergency repairs is an eight-pound sledgehammer. For real. To take that danged tight-fitting wheel off the hub when you have a flat tire on the road. And a 4x4, of course, so you don't destroy the wheel with the sledgehammer.

If the vehicle is pretty worn out, and especially if you're rough on vehicles, then you'd do well to have a pretty well-stocked toolkit in the vehicle with you.

If the vehicle and your driving style fall somewhere in the middle, then something between the sledgehammer and the SnapOn charge account will suit you better.

And... it also depends upon who might be called upon to use those wrenches you propose. I know a lot of people whose best use for wrenches is as props to hold up the "Help!" sign in the window. I know other people who can practically rebuild a bulldozer with a Leatherman.

What sort of problems do you anticipate that might require tools in the first place? Mull on that for a moment while I type.

You might... need to tighten battery clamps. 12mm or 1/2" end wrench. Battery brush. You might... need to replace a radiator hose (pretty unlikely these days, but you never know. For this you'll need a screwdriver or two. Pick 'em up at the parts place that sold you the hose. You won't be doing THAT with an end wrench. You might... blow a serpentine fan belt. 3/8"-drive ratchet and 3" extension to loosen the tensioner, no other tools. You might... blow a power steering hose. Crowfoot fitting wrenches to fit your longest 3/8" drive ratchet - you will NEVER get those hoses off with an end wrench. You might... burn up an alternator. You'll get pretty close with a set of end wrenches plus a ratchet to get that dang serpentine fan belt off & back on. You might... burn up a starter motor or its solenoid. NOW you can use your wrenches, at least until you need to get the little wires off the solenoid.

How likely is any of that stuff? When's the last time it happened to you? Much more likely is an electronic (sensor or controller) failure of some sort - you're not going to fix that on the road, no matter what you have for tools. When's the last time you even had a flat tire? Been a long time for me, so I leave the sledgehammer at home. In fact, the last two times I've helped other people change a tire, I had to SawzAll their spares out from under the vehicle - they were rusted in place, never had been touched before.

Do you really anticipate a bad battery connection? A blown alternator? Radiator hose? Serpentine belt? Really? Are you really ready to deal with any of these things on the side of the Interstate, hurrying to get it done before the tow truck gets there (the state police will call them without asking you)?

I don't carry tools any more. When I start driving my 1970 GMC full-time, I'll carry a few more tools... but not many, and probably specifically for some problem I anticipate having. On that truck, it's realistic that I could swap an alternator, change a belt, replace a starter motor or a radiator hose on the side of the Interstate in the pouring rain in the dark. Or a fuel pump. With three wrenches and a screwdriver.

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Modern vehicles use a wide range of tools for service work. Most countries in the world use the metric system of measurement, including the USA in many cases, yet there remains a legacy of the old Imperial system still around. A set of wrenches in the boot will not even get close to what you may need. If you have a particular job in mind you could carry the tools to carry out a repair - but how are you supposed to know the job will need to be done. A typical mechanic in a prestige main dealership in the UK, using typically Snap-On tools (favoured), will have a tool kit running into twenty to thirty thousands of pounds.

  • You're right. I should have specified more details. It is not my intention to be ready for an arbitrary task. But if I am stranded in the middle of nowhere, I'd like to maximize the chance that I can at least try to figure out what the problem is, or even patch things up enough to get to a dealership that has a twenty to thirty thousand pound toolkit. – Calaf Jul 29 '14 at 17:24
  • One thing I should have mentioned is to be a member of a breakdown service. Even though I am a professional in the UK motor trade I am a member of the CSMA, which is one. I have only used it twice in many many years(the wife ran out of petrol, and No.1 son had the wipers pack up). – Allan Osborne Jul 30 '14 at 10:24

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