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The correct stock size for threading 3/8-16 stud

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stioc

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#1
The machinery handbook says .375 for major diameter. I started with a .382 stud but by the time I got some depth to the threads the major diameter changed to .355 - needless to say the nut threads on very loose. So should I've started with say a .4" stud?
 

benmychree

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#2
No, start with .375" diameter and don't cut the threads undersize, as you apparently did; having said that there is nothing really wrong with having the stock a bit undersize, especially for coarse thread pitches. When I single point thread, by the time I am on size with the threads, I generally have to file off the crests of the threads to eliminate burrs, resulting in a undersize major diameter; little thread strength is lost by the insignificant reduction in diameter.
 

stioc

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#3
Thanks! I figured out my stupid mistake. The nut I was using to test the threading is an M10 not 3/8" :eek 2: Threw me for a loop and I was so proud of myself that I got all the angles and things right, the pitch was correct without looking any of that stuff up.
.
 

GoceKU

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#7
We have all done it, some metric and inch sizes are so close is hard to tell them apart especially on french and italian machines and automobiles, they use both system on the same part. Hair pull stuff.
 

benmychree

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#8
I recently had to repair a 2 1/2" steam valve, where the bonnet had broken; the bonnet was held on the body with 1/2-12 studs and nuts, the packing gland was fitted with 1/2-13 studs and nuts; I had tried a 1/2-13 not on the gland studs and assumed that it was all 1/2-13 ----WRONG!
After my discovery, I had to re make my parts to repair the valve, perhaps a half hour's work; "Could be worse, could be raining".
To see where this valve goes, Google "Sturgeon's Mill", and look at our web site.
 

Bob Korves

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#9
the packing gland was fitted with 1/2-13 studs and nuts; I had tried a 1/2-13 not on the gland studs and assumed that it was all 1/2-13 ----WRONG!
Joseph Whitworth strikes again! Well, not really. Whitworth was first to have accepted standards for fasteners... Still 1/2-12 threads are most
often Whitworth threads. Ask me how I know!

(British cars...)
 

benmychree

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#10
1/2-12 was our standard before World War 1, unless you were dealing with Brown & Sharpe, their standard was 1/2-14
 

benmychree

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#12
If we are talking odd ball threads, here is another one: I have a set of taps and dies that are nominally sized, but plus 1/32", like 5/8-11+1/32; they were used for threading pump rods and couplings when the old pumps were used that had the cylinder at the bottom of the well and the rod operated it from mechanism above ground, be it a windmill or power driven pump jack.
 

silence dogood

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#13
A 100 million + mars space went kapoot a few years ago because NASA forgot to covert from english to metric. :oops2:
 

P. Waller

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#14
One may purchase oversized and undersized taps for holes in parts that will later be plated or hardened.
 

benmychree

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#15
Yes, I had a set of them (oversize taps) at my shop, they were marked (+5), that is, .005 oversize. Some of our readers may not know that steel swells when hardened. Plating only effects the mouth of the tapped hole, at least in the case of relatively small holes due to the lack of circulation of the electrolyte through the hole, and I think a cathode is required in a hole plus circulation for effective plating in holes.
 
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