What Size BOB Trailer Nutz Do I Need?

Hello readers! This being my first venture out into the blog-o-sphere, I figure introductions are in order. Casey Clark here, Wandertec product developer and friendly neighborhood bicycle mechanic, at your service. Nice to meet you.

We received a call from a fellow the other day who was having a little trouble figuring out how to attach a BOB trailer to his bike, which has a solid, bolt-on rear axle. In fact, we’ve been getting quite a few calls and emails on the subject lately, which tells me that we’ve got a ‘teachable moment’ on our hands. I’m going to take off my Product Developer Hat and put on my Friendly Neighborhood Bicycle Mechanic Hat for a minute here and see if I can de-mystify the topic.

First off, the basics. A solid axle attaches to the frame via axle nuts, as opposed to a hollow axle with a quick release skewer. If you’ve got a hub with a solid axle, and you want to tow a BOB trailer, you obviously can’t use the standard BOB Trailer quick release skewer hitch, so what you need are some BOB trailer Nutz.


There are four sizes of BOB nutz available. To find out which one fits your bike, you need to determine your hub axle diameter and thread pitch. (If you’re not savvy to thread concepts yet, read this page on the Park Tools website). Measuring axle diameter is easy, set your calipers around the axle threads and get a reading. This is the major diameter, which is slightly smaller than the listed size. For example, a 10mm axle may measure at 9.8mm.

Thread pitch, or the frequency of threads along the length of the axle, is a little trickier to measure Like the article says, the best tool to use is a pitch gauge, but in a pinch you can use high quality calipers. Set your calipers for exactly one inch, and count how many thread crests fit between the caliper jaws. This is your threads per inch (tpi) measurement, which all SAE (a.k.a. “standard”, Imperial, English) axles use. ISO (metric) threaded axles don’t use a tpi measurement, but rather a crest-to-crest measurement. As far as hub axles go, the threads are always one millimeter apart, which would give you 25.4 tpi. Be careful differentiating between 10 x 26tpi and 10 x 1, they look very, very similar, but are not compatible. Generally speaking, 10 x 1 axles are only found on Campagnolo hubs and a few other brands that produced Campy copies.

This chart shows the most common rear axle sizes, the kind of hubs they are commonly found in, and the corresponding BOB Nuts part number as listed at Bike Trailer Shop. I lifted most of the info from the late Sheldon Brown. Remember, this is more of a rough guide than a comprehensive chart.


Axle dia./pitch Common Applications B.O.B. Nutz model


3/8′ x 24 tpi Wald, Skyway, coaster brake hubs, and hubs on many dept. store bikes. 3/8′ x 24 tpi


3/8′ x 26 tpi BMX, tandem, old Shimano XT (freewheel), and hubs on many dept. store bikes. 3/8′ x 26 tpi


9.5mm x 26 tpi (3/8′ x 26 and 9.5mm x 26 are generally interchangeable) 3/8′ x 26 tpi


10mm x 1 (25.4 tpi) Japanese Hubs (Suntour, Shimano, etc.), Miche 10mm x 1mm


10mm x 26 tpi Campagnolo, Campagnolo copies (Avocet, Ofmega, etc.) N/A


10.3 x 26 tpi Aka fg 10.3, a German standard, found on some older Sturmey Archer hubs 10.5 x 26 tpi


10.5 x 26 tpi Aka fg 10.5, a German standard, found on some older Sachs hubs 10.5 x 26 tpi

Once you have the right BOB Nutz, use them to replace the stock nuts, hitch up your trailer, and you’re ready to ride.


Well, I hope that clears up some of the confusion. If you have any more questions, you can always contact us directly, or ask your favorite local bike shop.

If we’ve left anything out please let us know in the comments below and we’ll update this post regularly to include it with any other new findings that we come across.

Thanks for reading, and thanks for riding bikes.

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