NAS bolt with tension nut

[PJYDE]

Hi all,

Follow up on my previous thread Link and a closed thread Link.

I have a NAS6603-16 bolt and an AN365-1032 tension nut with this setup:
AN-960L thin washer: 0.03125"
Material: 0.95276"
AN960-10 washer: 0.06250"
Total: 1,04651"

The NAS6603-16 has a grip length of 1" and T (thread length) of 0.345".

After torquing the nut I have about 1.5 protruding threads.

So this joint respects these rules:
- 1 to max 3 washers
- no threads in material
- 1 to 3 protruding threads
- nut does not runout

The specification of NAS66 shows that there are max 2 incomplete threads between the grip and thread part of the bolt.

The nut does not runout of threads, it takes more than 1 full turn to runout of threads (measured without having the bolt installed).

What is your opinion about the "2 max incomplete threads"?
(it could be that the first part of the nut is in the incomplete thread part of the bolt)

Many thanks for your advice!

 

[PJYDE]

Would anyone be so nice to share their thoughts about this?

The beginning of the threaded part of the bolt is allowed to have 2 incomplete threads.
I need more than 1 full turn before runout.
So if the bolt really has 2 incomplete threads the nut would start in the second incomplete thread.
But the the bottom of the nut has a chamfer of about 1 thread.
So the threaded part of the nut starts after the max 2 incomplete threads.
Is my conclusion correct?

(I don't find any exact specs of the AN365-1032)

Many thanks in advance!

 

[Worldtraveller]

I suspect there aren't really any issues with the installation as you describe it. You are probably within the nominal installation for this nut/bolt combination. I'm not sure you'd detect the incomplete threads if you continued to tighten the nut, since there is good threading through most of the nut at that point.

When you say you need more than 1 full turn before runout, I assume you mean as you tighten the nut into the shank of the bolt?

If so, you're fine, but I don't know that there's a hard fast rule for this. Unless your threaded portion of the bolt is very short, if you've got protruding threads within the usual spec, you should be getting full engagement.

 

[rb1957]

my 2c ...

your clamped up flanges are less than the grip. Washers on the threaded end should give the nut a proper seat in fully formed threads, ie washers pack under the nut so that the nut seats a min of 0.1" (assume 20tpi) from the grip length.

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

PJYDE... A few additional comments...

1. AN365-1032 NUT [obsolete PN] is a poor 'threading match' to the NAS6603-* bolt.

The AN365 has 10-32NF-3 threads.

The NAS6603 Bolt has 0.1900-32UNJF-3A threads.

There are several common nuts [MS21042-3 or L3] that have higher strength/toughness and have a much better thread match [in this case 0.1900-32UNJF-3A]... resulting in much better fatigue performance.

CAUTION 3/16 Dia Bolts are rather fragile and the shear-tension nuts MUST be installed [torqued] carefully so that the install is not over-tension-stressed... resulting in bolt stretch/distortion/fracture!!!

2. A rule of thumb [I use] for grip length determination is to calculate the min-to-max material dimensional stack-up [individual part thickness variations]... then select a grip length as close to the max stack thickness as practical... then specify a nominally thin washer for under the nut... but ensure that the installation allows washer thickness/stack variations during Assy to include: (a) one added washer any common thickness or (b) 1-to-3 alternate thicker washers ... for min material stack-up.

NOTE. I have seen mating part distortion/warpage, excessive primer/paint coatings [on multiple surfaces] and thick wet-sealant application cause stack-up problems that requires Assy considerations [not discussed here].

3. Thread protrusion... there is a lot of wiggle room on this.

Full locking engagement occurs when male/female [or external/internal] threads end at the same location. ALL bolt and nut threads have end-chamfers that shorten the possible engagement.

SAE ARP1515 requires an absolute minimum 'visible’ male/external thread protrusion’ of 1.5-T beyond the end of the end of the NUT.

USAF [and probably Army/Navy and most FAA maintenance documents]] requires minimum 'visible’ male/external thread protrusion’ of 2.0-T beyond the end of the end of the NUT. This is KISS for mechanics... but can create problems if OEM Assy and maintenance/mod practices vary for this 'norm', thus...

My company... to ensure maximum weight/mass savings consistent with tested/assured performance... requires minimum 'visible’ male/external thread protrusion’ 0.0-T to 2.0-T... male/external thread-tip dead-even with the top of the Nut to a max of 3-threads showing... on every installation. Any less is unsatisfactory from a nut-torque-tension-locking perspective... any more than absolute minimum is just added ‘dead’ weight.

CAUTION: Although my company’s installation practices produces a satisfactory threaded-fastener install at 0-T... this often conflicts with Acft, FAA or military acft‘general military’ Assy requirements. What a pain for us support/Depot guys.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Sparweb]

PJYDE,
Just to clarify about the threads, the forms UN and UNF are designed as machine cut, while the UNJF thread form is designed as a rolled thread.
Look up the FED-STD-H28/2 and MIL-S-8879 documents on the ASSIST website, and compare.
Looking back at the NAS660x bolt spec, notice the thread specification "SAE AS8879" which is based on the MIL-spec with the same number.

STF

 

[PJYDE]

Many thanks for your feedback.

About the threads, its clear now that an UNF but doesn't belong to an UNJF bolt due to the different shape at the root:

I searched if there's a nut with the same thread as the NAS6603 bolt and found MS21044, dash number N3 has a thread of 1900-32UNJF-3A, which is the same as NAS6603.

Would MS21044N3 work in tension?

Although according the specs it's clear that AN365 has UN thread, there is some confusion:
- Aircraft Spruce says "AN365 (supersedes MS21044) - cad plated stop nuts"
and
- the maintenance manual shows that a combi of AN365 and NAS6603 should be torqued to 25-30 inch/lbs

Could it be that the latest version of AN365 does have UNJF thread?

 

[WKTaylor]

PJYDE...

1. I checked several torque-tables VS the Cirrus-22 table You provided... Most of the torque values cited were a bit higher than I am used to seeing in my military applications for 3/16-bolts.

WARNING: be careful about tech data copywrite issues.

WARNING Hardware and torques will be substantially different for composite structures.

2. Common Nuts that I recommend for the NAS66*** [Stl-HT160+Cd]... for my all-metal MIL Acft...

In descending order of preference...

2.1 Shear application ONLY, low pre-tension

NAS679A*, NAS679X*

2.2 Shear-tension application, moderate pre-tension
MS21042L*
MS21042-*
NAS1291C*M

2.3 CAUTION, RE: MS200** Tension-fatigue bolts: my recommended nuts... and nuts on the C-22 table... in my opinion, are inappropriate for on these bolts [USE NAS1804-* or NAS1805-* + MS20002 washers]


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[PJYDE]

I found in the MS21044 specification the note that:

Interchangeability relationships: MS21044 nuts can universally replace AN365, MS20365 and NAS1021 nuts of like material plating and thread size.

Cancelled part numbers: AN365-1032, AN365-1032C, AN365-1032A, MS20365-1032, MS20365-1032C, MS20365-1032A, NAS1021N3 -> Substitute part numbers: MS21044N3

Link to the spec.

With that I conclude that AN365-1032 does not exist anymore and is replaced by MS21044N3, which has the UNJC thread, so is compatible with the NAS6603 bolt.
Is this conclusion correct?

 

[PJYDE]

1. AN365-1032 NUT [obsolete PN] is a poor 'threading match' to the NAS6603-* bolt.
The AN365 has 10-32NF-3 threads.

Please have a look at my previous posts.
It seems that AN365-1032A was replaced by MS365-1032A and later, in 1993, replaced by MS210443N3.
This MS210443N3 has UNJC threads.
When you order AN365-1032A at Aircraft Spruce, you will get MS210443N3.
So my conclusion is that when using the old name nowadays, you wil get a nut with UNJC threads and has the same thread as the NAS66XX bolts.
Agree?

 

[WKTaylor]

PJYDE...

"When you order AN365-1032A at Aircraft Spruce, you will get MS21044[highlight #CC0000]3[/highlight]N3."

Always remember a wise saying....

"You deserve to get what You ask for... but IF you don't ask for very much, don't expect to get very much".

IF You ORDER an AN365-1032A, but A.S.S. is sending You an MS21044N3... that must be explicitly stated in the sales agreement. NEVER 'just expect this substitution' to just happen because of the supersession trail You cited.

Dirty little secrets...

Older/obsolete parts were usually made by the thousands, just before the spec was obsoleted... and excess stock quantities were often 'socked-away' by surplus dealers for 'future quick sales'... may be decades later. I have seen 'new packages' of solid aluminum rivets [MS20470Dxx obsolete alloy] made in the late 1980s showing-up on stock shelves where I work... just last month.

Supersession is usually/always ‘toward the better’ [features/characteristics/materials, etc]... as opposed to ‘100% same as’. When this occurs, replacement becomes ‘a one-way street’. NEVER GO BACKWARDS WITH SUBSTITUTIONS... substituting an older/inferior [replaced] part for a new/replacement part will degrade the installation...

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[PJYDE]

Many thanks Wil.

I checked the inside dia of the nut and can confirm that it has UNJF threads since UNJF has a larger inside dia than a UNF threads.