OMI caboose truck screw size

Model Railroader General Discussion (Model Railroader)
1

I have an OMI NYC caboose that I’d like switch out the original brass trucks for Kadee Bettendorf metal trucks. Does anyone know right off hand what the size of the threaded hole is? It’s definitely smaller than 2-56. The original screw has a shoulder so it doesn’t seat very well for the Kadee truck. I’m guessing it might be 0-80 but I wanted to confirm that.

Thanks for the help…

Tom

2

Tom,

Many times brass imports have small ‘metric’ screws. IIRC, MicroMark has both metric & conventional(SAE) thread miniature screws. If you have a LHS that actually stock stuff like screws, you might want to take your model with you to do a ‘test fit’

I bought this metric assortment from MicroMark many years ago when I was working on brass models:

http://www.micromark.com/micro-screw-assortment-10-sizes-100-each,8545.html

Jim

3

Hi, Tom

My OMI caboose is the bay window job and it is made by Ajin Precision of Korea (OMI #3893) If yours was made by Ajin it may have a 2-56 bolster screw which is what mine has. It is a shoulder screw with a spring under the head. The truck bolster is just a thin brass channel.

Hope this helps and if you need any more info feel free to ask. Ed

4

If you have a micrometer you can measure the OD of the threads and maybe compare the value to a thread chart. Here is some info on “normal” threads, http://www.jimorrisco.com/index/thread-info-256910, and here is some info on metric, http://www.cefns.nau.edu/Groups/fabricationShop/documents/ThreadSizeCharts.pdf

5

I purchased a NWSL metric assortment at one time & it has come in handy.
However, I play CSI with things & have a couple ways to check.
I have a Screw Gauge metal plate in both SAE & Metric flats with tapped holes, not sure if it was from one of the Machining stores or MicroMark. ( I have also added some custom threads in blank areas).
I also have Thread Pitch Guages (like a Swiss Army knife with saw teeth = Pitch), that I can use, but when you get under the SAE 40’s it is hard to see those pitches at times.
Another trick I use; is to take a known good nut & test fit it onto the screw, sounds too easy, but really works good, if you can’t get a 2/3rd’s to a complete turn plus, it is the wrong size…
Thanks,

Chad

6

Thanks for the answers and suggestions, fellas. Yea, I could have/should have checked the major thread OD with my calipers. I just thought someone might know what the screw size was right off hand.

Ed, my caboose is also an OMI Ajin. I visually compared the thread OD of the brass shoulder screw that came with the caboose with a 2-56 screw I had in my stock and the 2-56 appeared bigger. So, I didn’t bother trying to test the 2-56 in the bolster. I’ll check it for sure this evening.

Tom