The Stovebolt Site Forums The Shop Area Engine Shop Motor mount bolt....

I need 4 9/16th-18NF-3 x 1 1/8 (or 1 1/4) inch bolts.

NF-3 is the kicker. Anyone know a source of these bolts?

Google has failed me.

I replaced my motor mount bolts with bolts I bought at a fastener store. I believe I later saw the same bolt at Ace Hardware. My truck is a 54. Not sure if the 49 uses the same.

Home Depot has grade 8. I would recommend them.

Grade 2-5-8 are strength ratings. Not the same thing.

Everyday bolts are made en mass on an automatic thread cutting machine... tolerance is very forgiving. These are NF-2 rated threads.

NF-3 rated threads are precision cut and have 0 tolerance.. that means the tolerance is +/- 0 (ie an EXACT fit).

The mounts are for a 1943 G506 1.5 ton truck.

I found the bolts but the are $6+ each +shipping. I'm just gonna drill/tap for 5/8-18NC and live with it that way.

Yes, it does. Why? Because the part is made with them. I didn't design it, GMC did (for whatever reason).

Part number GM-2202072 Insulator, engine support assy.
PN 081721 BOLT, hex head, s-fin, S, cd-plt (9/16-18NF3 x 1 1/8), insulator to frame and frame bracket)

ORD-9 SNL-G-508 July, 1945

That's why its needed

Welcome to the history books. NC (national coarse) and NF (national fine) are "standards adopted when we were working with British made fasteners. Two countries with shared measures and still the nuts and bolts would not fit together. Had to do with the thread profiles and clearances. So standards were introduced. Before World War Two, lots of manufactures made there own bolts and screws. After, there were fewer standardized fasteners. But as we all know...Some companies kept there manufacture and standards. Try to find a 1/4 24 screw. You can find 1/4 16 and 1/4 20 any where. Harley Davidson kept the 1/4 24 screw for a very long time. As pfarber pointed out there are standards still in place. And a big thank you for the explanation of the "class 2A and 3A bolts. Clears up some questions I have tried to answer for some time.

THIS chart shows all the tolerances for class 1,2 and 3 A and B treads for a WIDE range of threads.

Denny likely has the Machinist's Practical Guide handy, believe him .... but note that the American Standard specs for classes of fit changed in 1949, a bit after a manual from 1943

Bill

The tolerance is much tighter for the 3B (female treads) than for 2A (male threads). The slop will damage the mount parts.

3A is a much higher tolerance... they are typically not die cut, but cut on a lathe and not for mass production.

The NF-3 standard still applies today as you can get NF-3 spec bolts... although typically as cap head screws.

Don't tell the aviation industry that they are using outdated specs.... the AN system, for one, is also alive and well.

read for comprehension farber, I said nothing about the AN system, I pointed out that the standards were rewritten in 1949 [and a few times since], so individual specs and the parts made using them may be slightly or substantially different than what your parts based on pre-WW2 standards were .... consider how far backward compatibility works

Bill

OK, so show me where the NF-1,2,3 specifications have changed.... substantially enough for me to be wrong. You post a date.... but I'd like to see the tolerance differences... because even if they did change in 49, the pure, raw fact is that a class 2 bolt will tear up a class 3 nut.

I'll leave it to you to figure out what's changed over the last 70 years, here's from 2003: "This standard is the outgrowth of and supersedes previous editions that were published as B1-1924, B1.1-1935, B1.1-1949, B1.1-1960, B1.1-1974, B1.1-1982 and B1.1-1989."
http://www.ring-plug-thread-gages.com/ti-spec-ANSI-ASME-B1.1-2003-Changes.htm

Bill

Who told you this? The difference between class 3A and 2A is .0014" or less than a human hair. As per the Machinery's Handbook:

9/16"-18 NF 3A fit-Major diameter =.5625" max, .5538" min.

9/16"-18 NF 2A fit-Major diameter =.5611" max, .5524" min.


Manufacturing methods have improved a bit since that time as well and I think all they're trying to say is don't use cheap, poorly toleranced bolts.

This is getting ridiculous. Its admirable to pay attention to details but beating it to death doesn't benefit anyone. If a person has their mind made up so be it, but the bottom line is a good quality bolt will do the job also.

If you're willing to buy me another motor mount if I strip the treads with a normal 9/16-18 bolt I'll try it.

If you're right I'll put $20 to a local dog shelter in your name.

Up for it???

Ebay item # is 250890419977

I will buy you a new motor mount and give you $100 if it hurts your threads. I will give you a $1000 if they were actually made to 3A. The Aerospace industry I was in for 40 years used 2A and 2B. As pointed out, it's .10 of a frog hair. Put the money in the dog shelter. They probably couldn't hold that tolerance in 1945 in a Fastener shop in 1 out of 10. A looser tolerance bolt will fit a tighter tolerance tapped hole. (if the hole is even 3A to begin with) Thread designations have evolved a little as pointed out, and as evidenced by the fact that they did not use "A" after the 3 to designate male. BTW: there is no such thing in the general machining world as 0 tolerance. Especially in 1945. Everything has a tolerance or there would be untold waste at the inspection table. Non-interchangeability of parts would make Henry Ford roll over in his grave. The machines have tolerance, the humidity & altitude will play a roll. Some fine EDM, chem etch type metal removal can produce good, tight, cosmic, nuclear, micro, plasma, Zombie tolerances. But not screw threads.
To say that the 2A is tighter tolerance than the 3A is a misnomer. They have the same tolerance +/- .00435. The 3A is spec'ed to the exact screw size (9/16).5625 and the 2A is not. The 2A bolt is not as large. The correct terminology is the 3A has less allowance.

Same chick, different skirt. Slap one in and drive already.

If its a little tight, we'll call it a lock nut. Get some sleep fellows. There may be a worthwhile topic to discuss tomorrow.

It's Farber's fault, he got us all cranked up. I don't think slapping women is the answer Hollow. Calm down.

That's not what I meant... Want me to send you $6.00 for the uber tolerance or allowance bolt?

You can't argue with someone who knows they're right.

So much misinformation... since you are guessing I'll skim over the obvious errors:

The parts manual does not need to specific as to A or B, it said BOLT... plus its NOT a print, its a PARTS MANUAL. So strike 1.

They could not produce parts to the limit? ARE YOU SERIOUS? I have already supplied two parts that ARE machined to the spec. In mass production quality. Plus the parts WERE PRODUCED FROM 1943 to 1961. I have them in my hand... I can gauge them if you like... but it'll cost you because you are blowing smoke in face of reality. Strike 2 and 3.

NF-2 and NF-3 tolerances change as bolt diameter change. You did know that right?

1/2-13. 2A 0.5000 0.4985 0.4876
1/2-13. 3A 0.5000 0.5000 0.4891

5/8-18. 2A 0.6250 0.6236 0.6149
5/8-18. 3A 0.6250 0.6250 0.6163

Looky there! Not the same for every bolt at every size.

Strike eleventy billion.

I've proven my point.

Oh yea, I worked in SubSafe a Nuclear QA... so yeah... they DO make bolts to that tolerance even way back in the 40s.

Farber, this is really greasy spoon stuff and I don't want to be rude, But every time you post after too much coffee and you've been watching the word series (strike 1,2,3), you misspeak while trying to insult. No one has said that the tolerances are the same for each SIZE bolt, just each bolt's 2A tolerance is the same as it's 3A tolerance. Take a breath and go back and read carefully. Also you do not have the equipment to "gauge" the Major, Minor and Pitch diameters of screw threads to see if they are in tolerance. You know that right? You are also confusing us when you say you are looking for a place to buy 3A bolts and you have "supplied" them to someone already. I am not guessing about anything nor trying to blow smoke, just can't let you rant without rebuttal. Some people get real mad when they realize they are wrong and some apologize. If you are pulling my leg, it hurts now. Take care. Try the 2A and see if it feels like it's too tight or interfering. Where are these bolts used, how many? Maybe I can help if I know that. Do you understand that you are wrong also about the 3A having no tolerance? as in "+/- 0" ?

I think your idea to drill and tap larger is viable.

As for strike 1,2,3...Your batting average is not so good.

Bout time to turn the key on this one.
DG

too bad he doesn't know not to paint his distributor.

Confucius say "Real knowledge is to know the extent of one's ignorance."

Confucius never had to figure out how to find the correct bolt. He just thought up sayings all day.

I agree with Denny!

I agree the post is a little off track. But it is mostly on track except for people posting that they can't stand to read it.
Why does a post bother members who don't participate? Why do they post just to say to us "stop posting". How does it bother them? Why don't they read it and move on? Too many chiefs. Too many sad, non humorous, strict, old guys. Leave us alone, we are OK. Saying it's enough then piling on to say you agree it's enough, is extending the post. Go tell your mommy on us.
This forum is turning into the only thing I can post is what someone else thinks I should post. We have a section on here with 150,000 post telling "what you got done on your truck today" , read that. I have never posted a post just to tell others to stop posting. That's absurd. I'm sure my complaint will be removed.

I have experience in exactly what machining practices are required to obtain a USN level 1 subsea vendor designation/qualification and it is no easy feat. That being said aren't we supposed to be having fun building old trucks and not nuclear submarine toleranced devices

I always thought these trucks were meant to be simple. Now I am worryng!

Not sure what "insulator to frame and frame bracket" is. Haven't seen anybody have this problem before? Hope he has worked it out. They are simple and long lasting, unlike some of todays vehicles. A 1947 truck is still going after 66 years, will a 2000 truck still be going in 2066? No they won't, but part of that is that they are not unique anymore so we "throw" them away.

I check out this thread once a day, after putting on knee-high wading boots. I've learned at little - thanks, Denny, and non-emotional others.

I guess some just make unnecessary, cute, snide comments and non-emotional gotcha's. How rewarding it must be to be so intelligent.

And some.....are all knowing.
DG

I was taught by my Dad that you have to learn how to learn. Once a person understands that the facts come easy and can be decifered.

Yes "Pot", I am black.