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Old Sep 02, 2013, 10:54 AM
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Push Rods and Threads

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A 2-56 rod is supposed to be a #2 diameter thread with a pitch of 56 threads per inch (TPI). That is a nominal .086" diameter (44 Gauge) for a class 2A thread. The class determines the thread depth with a lower number being less depth and strength and a more sloppy fit. Number sizes are in .013" increments so a #1 would be .073" and a #5 would be .125" (1/8"). All of the factory rods I have seen have a ROD size of .072". I think the threads are rolled and not cut at the factory. I am guessing that rolling will squeeze the hot metal to form the threads. If we thread this rod with a 2-56 die, the thread size would be cut to .072 instead of .086". This would be a loose fit and not as strong. It looks like to cut your own threads you would need a .086" rod diameter.
This chart: http://www.engineersedge.com/screw_threads_chart.htm
does show a minor diameter of .0635". Does that mean that threading the .072" rod with a 2-56 die is plenty good for strength? Has anyone done this and had a rod pull out?
Do the metric rods have the same problem?
Does anyone know the thread pitch of 1.3mm rod and where a die can be purchased? Will the rod diameter be too small to cut the threads to the proper diameter like the #2 rod?
I have some Hobby King unthreaded rod that measures .058" diameter. Best I can measure, could be .0582? What die would be used to cut threads for this rod? Are there any ball links that would fit this?
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Old Sep 02, 2013, 12:05 PM
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Joined Sep 2011
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BA Outer
Diameter[1]:7, 16 Threads
per inch Threads
per mm Tap drill
0 0.2362 in / 6.0 mm 25.38 1 5.1 mm / 7 gauge
1 0.2087 in / 5.3 mm 28.25 1.112 4.5 mm / 16 gauge
2 0.1850 in / 4.7 mm 31.35 1.234 4.0 mm / 21 gauge
3 0.1614 in / 4.1 mm 34.84 1.372 3.4 mm
4 0.1417 in / 3.6 mm 38.46 1.514 3.0 mm
5 0.1260 in / 3.2 mm 43.10 1.697 2.65 mm / 37 gauge
6 0.1102 in / 2.8 mm 47.85 1.884 2.3 mm
7 0.0984 in / 2.5 mm 52.91 2.083 2.05 mm / 46 gauge
8 0.0866 in / 2.2 mm 59.17 2.330 1.8 mm
9 0.0748 in / 1.9 mm 64.94 2.557 1.55 mm
10 0.0669 in / 1.7 mm 72.46 2.853 1.4 mm / 54 gauge
11 0.0591 in / 1.5 mm 81.97 3.227 1.2 mm
12 0.0512 in / 1.3 mm 90.91 3.579 1.05 mm
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Old Sep 02, 2013, 12:09 PM
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I don't think 1.3 mm die is standard size.1.2/1.4 are.BA is metric based.
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Old Sep 03, 2013, 07:07 AM
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I've been cutting my own 2-56 and 4-40 threads for 20 years and never had a thread skip or strip. Always back up a metal clevis with a nut and lock washer.
Edwin
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Old Sep 03, 2013, 07:31 AM
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What size rods do you use?
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Old Sep 03, 2013, 07:43 AM
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Dont know right off the top of my head. They are leftover cuttings from pre threaded rod. There are two types, one is very hard and cannot cut threads into it, the other is soft enough to cut threads yet hard enough to use as pushrods.
Edwin

The hard ones are shiney, the softer ones are a dull grey.
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Last edited by edwin1; Sep 03, 2013 at 08:55 AM.
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Old Sep 03, 2013, 11:17 AM
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I am guessing the shiney ones are stainless steel. Can you measure them sometime and post back when you have a chance?
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Old Sep 03, 2013, 01:16 PM
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Dull grey;
2-56 is .073
4-40 is .092
Shiney steel (pre cut threaded ends);
2-56 is .073
4-40 is ??? I didnt have any in my parts bin.

When I need both ends threaded on the shiney steel, I use the solder on threaded ends. Soldered correctly, they wont come off.
Edwin
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Old Sep 03, 2013, 09:11 PM
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Thanks!
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