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I am trying to buy bolts for mounting the tub of my M38 to the chassis. Page 292 of ORD 9 SNL G-470 Lists the following bolt for example. BOLT, MACHINE, hex-hd, S. cd or zn-pltd, 3/8-24NF-3 x 1. All is understood in this designation except the -3 x 1 following the NF. Can someone tell me what the -3 x 1 stands for? I've spoken with multiple nut n bolt suppliers and no one seems to know. One guy suggested it was a 3" bolt with 1" of thread, but as an example another bolt is listed with a -3 x 7/8, which doesn't seem a standard. Others are clueless. Any wisdom is appreciated.

Just from what I've seen from removing old bolts......the first number is the diameter of the bolt.....the second is the number of threads oer inch.....the third number is anybody's guess.....and the fourth is the length. I've tried to correlate that 3rd number too with no such luck. Might be the grade rating of the bolt but from what I've seen so far what's not grade 8 is grade 5.....and everything else bears no grade markings at all. I'm sure somebody on here knows....fur shure.

Jim

If I recall the 3 may refer to the class of fit 3 being medium as per the American National Standard. the x1 would indicate the length in inches. The fit classes were 1 - 4 loose, free, medium, close.

That was a bear to look up because of the updated standards but SteveJ is definitely on the right track.

Class 1 changes to 1A (Loose) for external threads or 1B for internal threads
Class 2 changes to 2A (Medium) for external threads or 2B for internal threads
Class 3 changes to 3A (Close) for external threads or 3B for internal threads

Here are some links that help out:

Note the reference to "military" in this one:
http://www.sizes.com/tools/bolts_inch_threadFit.htm

the big scoop:
http://www.ring-plug-thread-gages.com/ti-N-vs-UN.htm

Hope this helps,
Cody

Cody,
Nice work!

Thank you all. Very helpful. Apparently the body to frame bolts require a higher stress tolerence than others! One last question, though. What is the difference between internal and external threads?

Well that's cool.......so the thrid number defined how tight the hardware went together. Now this begs me to ask.......whenever we're rebuilding something on one of these jeeps.....should those 50+ year old nuts and bolts be replaced (because there's no way they are a 3 anymore) with new stuff......and if so.....how do you get a 3A (or B) fit these days when you just go to the store and get an appropriate nut and bolt and slap em together? Great.....just what I needed....something else to worry about!

So, do I think as confused as you look I am?

Jim

What is the difference between internal and external threads?

The internal threads are in the female part (Nuts, castings) of the object and the external threads are on the male part (bolts and studs).

The close tolerance controlled by this 1, 2 or 3 is only one of many mechanical standards and tolerances used for hardware.

This 1, 2 & 3 stuff only refers to the matching of threads.

We also have tolerances for fit in attached material, which is where the shank part of the bolt comes into very close tolerance sizing issues.

We also have hardness standards , which is where bolt grades come into play.

You will need to consider all of these when substituting bolts and nuts on your jeep.

The simple rule is what you use must equal or exceed the original items quality and strength.

As a basic rule of thumb try to stay with grade 5 or higher on all hardware which is placed where if it fails it may cause serious damage to equipment and/or serious injury or death.

You can usually rely on hardware with a military spec. IE prefaced by AN or NAS or MS.

should those 50+ year old nuts and bolts be replaced (because there's no way they are a 3 anymore) with new stuff

Unless there is a service note, TB, MWO etc from the using authority (IE Army) or the manufacturer (IE Willys, Kaiser, Prestolite, Auto-Lite) recommending upgrading a piece of hardware you need only meet the original standard.

.....and as I understand it......arbitrarily using a grade 8 in place of a grade 5 or a grade 5 in place of a lower grade simply because it seems like a "better" connection is not necessarily true. One of the things that the harness gauge of the original hardware is based on is the anticipated failure of the hardware in lieu of material failure of the components that they attach. Like I guess it would be better to sheer a spring shackle bolt and have to replace it then it would be to rip the shackle mount from the frame or worse yet bend the frame beyond servicibility. Also.....it seems unless you go ballistic and buy the really, really expensive stuff....the harder the grade of the hardware the more susceptible it is to corrosion and oxydization. So replacement of a 5 bolt with an 8 could mean you're looking at having to change it out again sooner then you would had you used a replacement 5.

Cool stuff hardware.......or maybe I just need to get a real life.

Jim

There are a couple of old publications in the form of small handbooks that are great for this kind of stuff. All the basics for fasteners, tools and hardware.
I am sure Wes has them tucked away somewhere as I do and have since I was an apprentice.

Standard Aircraft Handbook = Leavell & Bungay

Standard Aircraft Workers Manual - Fletcher Aircraft:)