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I have a spare six-point 3/4" flank drive socket I'd like to keep in the trunk with a breaker bar. (From recent experience, the little collapsing wrench that comes with the seventh-gen Chevy Malibu doesn't provide enough torque to loosen the lug nuts, when changing a flat tire. It's possible they were over-tightened.)

The lug nuts are presumably 19 millimetre. Is this an acceptable idea, or is there a real chance I'll be abusing the lug nuts by using a socket 0.26 % (a quarter of one percent) too big?

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  • Why are they presumably 19mm? Are you unsure? Is your 3/4 socket a 12 point or a 6 point?
    – DucatiKiller
    May 13, 2016 at 5:33
  • Six-point. Forgot to mention that, sorry. Edited the question.
    – Mathieu K.
    May 13, 2016 at 14:38
  • Yes, I'm unsure. I read somewhere that cars made in the last few years (15?) use metric sizes, but the user's manual doesn't say what size the lugs are, and I don't have a micrometer.
    – Mathieu K.
    May 13, 2016 at 14:40
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    I do it all the time in the shop, .75in= 19.05000mm, not exact match but good enough for me
    – Moab
    May 13, 2016 at 18:06
  • Just like using a 13mm on a 1/2 nut, 8mm on a 5/16, 16mm on a 5/8, etc... but this one is an even closer match. Great numbers to remember when you're stuck using open ended wrenches on tight metric fasteners - just going the other direction :)
    – Lathejockey81
    May 14, 2016 at 15:56

2 Answers 2

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Being as it's only 0.05mm larger in diameter, you shouldn't have a problem unless you're using that socket on a rattle-gun every day. If it's a 6-point socket, the wear on the nut should be minimal (12-point sockets have more of a chance at 'rounding' the nut).

Ideally, however, you should go down to the shop and spend two dollars on the correct sized socket. Yours will still get you out of a pinch if needs be however, and using it once or twice shouldn't be too bad for the nut depending on how tight it is.

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  • The tightness is the problem. They're supposed to be tightened to 100 lb ft, but the people at the shop will tend to do whatever they want. Trying to loosen, say, a 120 lb ft nut with the short (18-inch?) wrench sounds problematic.
    – Mathieu K.
    May 13, 2016 at 14:46
  • @MathieuK.: With that much force to torque with, I'd get a proper 19mm socket if that is indeed the size of your lugs. No reason not to, really, since the socket itself should be inexpensive.
    – Ellesedil
    May 13, 2016 at 20:35
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    .05mm < .002 in. That's less than a hair, and well within most manufacturing tolerances on precision machined surfaces... which a socket is not. No, there's no need to get a 19mm socket, and it will present no difference in performance just because the number on the side is different.
    – Lathejockey81
    May 14, 2016 at 15:51
  • @Lathejockey81: You're the first to mention the tolerances to which the socket is machined. Excellent. Please re-post as an answer. The wording is fine.
    – Mathieu K.
    May 15, 2016 at 17:36
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Lathejockey81's comment on the other answer:

.05mm < .002 in. That's less than a hair, and well within most manufacturing tolerances on precision machined surfaces... which a socket is not. No, there's no need to get a 19mm socket, and it will present no difference in performance just because the number on the side is different.

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