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More and more trucks in the UK seem to have these yellow triangles on the wheel nuts. Usually in pairs pointing at each other, but I have seen one truck that had them all facing the hub.

What are they for?

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If you are talking about these, they are there to indicate the torque or the bolt has not loosened any. They are just an easy visual sign the lugs have not loosened any.

Part of the way down on this page which reviews lug nut torque indicators, it says:

To assist with making sure that there are no loose lug nuts on a truck which can give rise to "wheel separation accidents," there is an invention that we call "lug nut torque indicators" that we have seen installed (mostly on the steer tires) of some trucks. The Wheel-Check.com website refers to these as "loose wheel nut indicators."

EDIT: Just so you know, they are becoming prevalent here in the US as well.

EDIT2: For better understanding, these are put on after the lugs are torqued, in a recognizable pattern. If a lug should turn (and thus have lost torque), it would immediately be visually recognizable as such.

  • How do you know the torque is off? How do they indicate? – DucatiKiller May 15 '16 at 17:46
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    That's why you install them in a recognizable pattern (2 pointing at each other, for instance). If one of the nuts is loose, the indicator rotates with the nut and it no longer points in the right direction. – Hobbes May 15 '16 at 17:49
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    We used to do this all the time on (Original Equipment Manufacturer) OEM pre-production test vehicles where torque is critical (not just on wheel lug nuts). We'd use a paint pen to draw a straight line on both the bolt (or nut) and the thing it was attached to. If you saw a break in a straight line, you knew a bolt was getting loose. Every fastener on a test engine got this treatment. – zipzit May 15 '16 at 19:19
  • @Hobbes Thanks for filling in the missing piece. I didn't get that part. – DucatiKiller May 15 '16 at 22:07
  • That's pretty clever, why don't cars have this? Are such accidents more common with trucks? – I have no idea what I'm doing May 16 '16 at 10:18

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