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Lex’s recent post on captive nuts reminded me of some other nuts I’ve been using a lot lately while doing some volunteer work on a search-and-rescue van: nylon-insert hex nuts. Depending on which big box you shop at, and whom you ask when there, they’re also called stop nuts, locknuts, or nyloks (although NYLOK® is a nylon material typically applied to bolts and screws), or nylocks. I like them because they resist vibration and loosening, they’re reusable, they don’t damage threads, and they’re readily available. McMaster-Carr has a large variety in their catalog, and many of the big boxes carry Hillman versions.

For higher vibration, temperature, or safety applications (like motorcycle and automobile racing or aviation), safety-wired nuts, or nuts with cotter pins are the preferred — if not required — choice. Other alternatives include two-piece thread-clamping locknuts and distorted-thread locknuts.

A 100-piece package of 1/4″-20 nylon-insert nuts will cost you around $5.

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22 Responses to Nylon-Insert Hex Nuts

  1. Paul Bob says:

    Harbor Fright has box assortments of these. They are quite cheap when they are on sale.

  2. ToolGuyd says:

    I absolutely hate nylon locknuts. I don’t quite remember why, but I try to use suitable alternatives whenever I can.

  3. fred says:

    For vibration dampening along the axis of a bolted connection – you might try a Belleville washer approach:


  4. jeffrey immer says:

    i personally like the spring type washers when i have a choice it’s seems like starting the nylon ones can be difficult if you are hand starting

  5. Toolaremia says:

    Gordon, love ’em. Though they shouldn’t really be reused in applications where things falling off would be Bad™.

    Hey Paul, nice to see my “Harbor Fright” love/hate name is catching on. 😉

    ToolGuyd, I’d like to know why you hate them. Haven’t had any pique my hate. Is it because they aren’t pretty and “nylon” ain’t manly?

    Fred, I learned something today thanks to you! Knew they existed, didn’t know what they were called.

  6. george says:

    they are ok. but they and heat don’t get along. most times i just prefer using loctite.

  7. kyle says:

    i hate them in aplicatins where they have to be screwed on to a threaded rod because it is a pain to use a wrench to tighten it dwn for 12 inchs

  8. joe says:

    Careful using power tools to install them, ie: drill driver, impact driver, etc. The speed can melt the plastic causing the nut to seize on the bolt making it pretty hard to get off.

  9. Old Donn says:

    What George said. Got these with the locking collars on my motorcycle exhaust. After the 1st ride, guess what.

  10. John Eisenhower says:

    I thought that these nuts were not reusable so I googled it and found some FAA information on them:

    Recommendations for use per FAA AC43.13-1B Acceptable Methods and Practices:

    * Elastic lock nuts are not to be installed in areas exceeding 250 degrees F.
    * Do not reuse elastic lock nuts if the nut cannot meet the minimum prevailing torque values shown in the chart
    * Do not use self-locking nuts on parts subject to rotation
    * Do not use self-locking nuts where the loose nut, bolt, or washer may fall or be drawn into the engine air intake scoop.
    * Do not use self-locking nuts to attach access panels, doors, or any parts that are routinely disassembled before or after each flight.

  11. Kris says:

    I thought the name of that fine establishment was “Horror Fright”?

  12. rob says:

    well they are also only a grade 5 at best
    so if your using them any where that has a pretty
    heavy load or anything that needs grade 8 your not going to be able to
    get away with it

  13. ambush says:

    Loctite doesn’t work when it gets hot.

  14. browndog77 says:

    Two nuts, torque them together, locked for life! Nuff said.

  15. Joe C. says:

    Double-nutting isn’t all it seems to be. The outer nut is susceptible to vibration just like a single nut torqued against whatever you’re securing. The only “locked for life” options are properly used safety wire, or welding.

  16. fred says:


    How about a castleated nut and a cotter pin?

  17. george says:

    for heat i use copper metal lock nuts. each situation has its prefered way to secure bolts/nuts.

  18. Brau says:

    I used to buy these until I discovered medium bond Loctite. The nylok’s often become oily or worn and don’t lock, but the locktite always works with a bit of cleaning and can be used on any size nut.

  19. Joe C. says:

    Yeah, fred, I missed that one.

  20. Paul says:

    Typically in aerospace uses, all metal locknuts (usually called self-locking in the biz) are used. The locking feature is that the thread is deformed into an oval shape, uses the spring properties of the metal squeezing the bolt’s threads to lock. In many cases, we still put a locking device in addition to the self-locking fastener, lockwire, locktabs, cotter pins, etc (called positive locking).

  21. Keith says:

    Anti vibe nuts – I like them. No, they’re not good for heat, but for
    other applications (such as applications with a lot of vibration),
    they’re perfect.

    I use them to replace the factory fasteners that vibrate loose off of my

    Especially those oversize ‘wing’ nuts on the push handle that are
    supposed to allow the handle to fold; mine just vibrate off and get lost
    in the lawn somewhere.

    I found these nuts with the nylon inserts to be just the ticket, since I
    don’t need to fold the handle.

    I give them two thumbs up.

  22. melvin says:

    You can buy grade 8 nylocks. I’ve got a bag full of 5/8ths grade 8 nylocks along with matching grade 8 carriage bolts for a special application.

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