We got a dynacraft kids bike for my daughter off facebook market, but need nuts to attach the training wheels. The ones we have don't seem to be threaded right or something (won't tighten all the way without becoming loose again, like the threads are slipping).

I've looked everywhere online but can't find anything saying what kind of nut it should be. How can I go about figuring it out? Dynacraft won't let me contact support without a serial # and I see no serial # on the bike anywhere.

  • What kind of wheels do you have? What kind of nut did you try? Commented May 1, 2021 at 21:00
  • 2
    There are a dozen different schemes for attaching training wheels. Either visit a bike shop or post some pictures. Commented May 2, 2021 at 1:01
  • You said the existing nuts aren't a good fit. Is the axle thread damaged already ?
    – Criggie
    Commented May 2, 2021 at 1:34
  • BTW, the serial number is often on the bottom of the "bottom bracket" housing. Commented May 2, 2021 at 2:17
  • 5
    Consider leaving the trainer wheels off. Seriously, tey cause more problems for young learners than they solve. If needed, remove cranks and turn bike into a balance bike to start with.
    – mattnz
    Commented May 2, 2021 at 3:24

2 Answers 2


The other answer is functional, but buying tools to check threads is going way beyond what someone needs who just wants to put training wheels on a bike. Assuming you are in a North American country, head out to the nearest hardware store (Ace, True Value, etc.) or home improvement store (Lowes, Home Depot, etc.) and bring the training wheels with you. Its possible that the threads are destroyed on either the nut or bolt. The employees at these stores are always helpful and can find exactly what you need, or sometimes see issues that you can't. If employees aren't there or not helpful, there are usually nuts and bolts in the hardware section you can use to test out different sizes for fit.


In brief, you need to identify the major diameter and the thread pitch. That should be sufficient. Secondary considerations like the thread's form, its minor diameter, are less important. This also assumes the existing thread is not damaged.

  1. You will need a vernier caliper - a ruler is not accurate enough, though a cheap plastic vernier may work.
    enter image description here

  2. You need a thread gauge. Bicycle threads are frequently Imperial (because reasons) but not always. And its possible that the wrong thread might be close enough to go on but not tighten properly. IE the difference between 24 and 26 TPI only shows up after a couple of turns of the nut.

From Parktool link below

The known sizes are:

Spec Common use
5/16 inch x 24 tpi Front hubs, solid axle, less expensive bikes
8mm x 1mm front solid axle hubs
3/8 inch x 24 tpi Some solid axle bike, including coaster brake
I would suspect this one, but no guarantee
3/8 inch x 26 tpi Solid rear axle
10mm x 1mm Some Quick-release rear axles
10mm x 26 tpi Rear axle, quick-release, Campganolo® (weird metric+imperial)
14mm x 1mm Uncommon - BMX stunt bikes

Useful link: https://www.parktool.com/blog/repair-help/basic-thread-concepts

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