I'm rather intrigued by these washers: enter image description here enter image description here

What are they called?

  • 1
    Shakeproof washers. Commented Nov 29, 2021 at 22:44

3 Answers 3


It's a serrated lock washer. I've seen them used for two purposes:

  1. Locking the nut in cases of vibration.
  2. Ensuring a electrical bond on painted or corroded metal.

Or, of course, a combination of the two. They are mildly effective against vibrations, and properly torqued very effective to ensure an electrical connection.

  • 8
    They are also useful in situations where you cannot get a tool on one side of a nut and bolt. If you put one of these washers behind the nut, and if you can hand tighten to the point where the lock washer starts gripping, you can usually then fully tighten the bolt without holding the nut.
    – jay613
    Commented Nov 29, 2021 at 14:10
  • 1
    @jay613 I've had a few cases where all I could get on the nut side was long-nose pliers, end on. That's nowhere near enough to torque up the fastener alone, but as you say is enough to get the washer to bite
    – Chris H
    Commented Nov 29, 2021 at 15:59
  • Pedantically, an "external tooth lock washer".
    – user101382
    Commented Nov 30, 2021 at 19:03

They're anti-vibration locking washers, the teeth digging into both the nut and whatever it's holding. They are also available with the teeth on the inside (as the pic), rather than as shown above, the outside.

enter image description here

  • Honest questions: How can you tell that the teeth on these are on the outside? What happens if one just puts the washer on upside down, wouldn't that put the teeth on the inside? How does one know if one needs teeth on the outside vs inside for any given application?
    – FreeMan
    Commented Nov 29, 2021 at 13:00
  • 11
    @FreeMan - I meant the teeth can be round the hole in the washer rather than on its circumference. Come on!
    – Tim
    Commented Nov 29, 2021 at 13:02
  • 6
    Oh! Gotcha. Sorry, I'm still on my first cup of coffee and that inside vs outside frankly didn't occur to me. Also, first day back after vacation - my brain is still in the sun on the beach. I probably shouldn't answer too many questions this morning...
    – FreeMan
    Commented Nov 29, 2021 at 13:08
  • The more important question is "how does one source either variation in Eastern Europe?" Dang, these things are hard to find... Commented Nov 30, 2021 at 20:13
  • @SO_fix_the_vote_sorting_bug searching your local/online suppliers for "lock washers" or "locking washers" doesn't turn up anything? May need to translate as appropriate of course. Also try local synonyms for words like "gripping" or "retaining" (though the latter might get you other results)
    – Doktor J
    Commented Dec 2, 2021 at 19:08

They are spring locking washers.

They are designed such that the "teeth" oppose the nut vibrating loose.

  • 1
    Ah, now there y'see a spring lock washer means something different to me; I think an SLW looks more like someone cut a single coil off a spring and squashed it..
    – Caius Jard
    Commented Nov 30, 2021 at 16:50
  • 1
    A machinist might know what you are talking about if you had a box of these, but if we are being pedantic spring lock washers are conical and have serrations or ribs that help grip (i.e., no teeth around either circumference). What we see above is a toothed lock washer. Other common kinds of spring washers are split lock washers.
    – user101382
    Commented Nov 30, 2021 at 19:00

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