NAS7404-10 4

[daxmann]

Good morning all,

I'm trying to find the spec for NAS7404 and keep striking out. I have even went to the company owner to purchase it and he tells me he can't find it. This is a 100deg countersunk screw and I need to add the O/D of the csk after drilling. Can someone please point me in the right direction? Thank you.

 

[monkeydog]

IHS does not have it, are you sure of the spec number?
Why not ask the company owner for a copy of the drawing he is making the screws to?

 

[WKTaylor]

Daxmann...

NAS7404 is actually embedded within AIA NAS7400--7416 [2012.11.30] BOLT, SHEAR, 100° FLUSH HEAD, RIBBED CRUCIFORM RECESS, CLOSE TOLERANCE, ALLOY STEEL, SHORT THREAD, SELF-LOCKING AND NONLOCKING, 95 KSI Fsu - Rev. 4

The spec sheet is available thru AIA or thru a number of sources on the web.

http://datasheets.globalspec.com/ps...ociation/B4DFC411-7DC6-49E2-9E34-594E66663469

My company has a subscription for IHS-Global 'Standards Expert' that has this spec and thousands more aerospace related specs for subscription down-load.

The following catalog has a rough but adequate sketch of the 'part family' NAS7400--7416.... amonge several hundered common 'part families'.

http://files.engineering.com/getfil...dwr~Product_Gd_July2003~Illustrated_Parts.pdf

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[daxmann]

Amazing! Thank you so much wktaylor, you are a big help.

 

[Sparweb]

Thanks Wil,
I'll also find that handy.

STF

 

[WKTaylor]

BTW...

NAS7400--7416 BOLT, SHEAR, 100° FLUSH HEAD, RIBBED CRUCIFORM RECESS, CLOSE TOLERANCE, ALLOY STEEL, SHORT THREAD, SELF-LOCKING AND NONLOCKING, 95 KSI Fsu

NOTE. An important descriptor is missing from the title: spec includes NOMINAL Diameter, 1st-OS diameter [+1/64"] and 2nd-OS diameter [+2/64"] for repair purposes.

NAS7404-10 = Forged flush tension [full depth tension] head steel bolt, X-recess drive, cad plated, nominal 0.2485--0.2495-Dia shank, Short [0.250-28-UNJF-3A] rolled threads, NO locking element, NO Cotter-pin hole in threads. Procurement spec [how it is actually made] is per NAS4002.


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[daxmann]

Wow, how can you know so much about this? Did you write the spec? Thanks again.

 

[tbuelna]

daxmann-

Your NAS7404 bolt has a .250-28 UNJF thread with a close tolerance body and full size 100deg flush head. I have a copy of NAS1204 bolt specs which should have identical dimensions for the head. The height of the head ("H") is 0.106" REF. The actual (truncated) OD of the head ("B") is 0.449" MIN. The head OD to theoretical sharp corners ("A") is 0.507"/0.497" REF. The included angle of the head is 101/99 degrees. So call out a nominal 0.500" dia x 100deg c'sink.

The only thing you need to watch for is there are some NAS 100deg flush bolts that use a "reduced" head, where the head OD and height are smaller than a full size head NAS 100deg flush bolt. The words "reduced head" are normally included in the spec title for these bolts (see NAS1581). And since the title listed above by wktaylor does not include those words, I think it would be safe to assume your NAS7404 bolt has a full size head.

Hope that helps.
Terry

 

[daxmann]

Thank you Terry, you are correct they are full size heads. Using one of wktaylor's links the owner was able to purchase the spec. I just want to say thank you to everyone for the helped.

 

[WKTaylor]

daxmann, Tbuelna...

This bolt style is an attempt to save weight in older designs and is part of a bolt-style evolution. Correct this is a full size tension-head fastener... but with short threads, so that ONLY a lower strength low-height shear nut [EX: NAS679] or a very low-height shear-tension nut [MS21042, NAS1291] can be installed.

In the 1940s only flush bolt style available was full-depth tension style head with long threads + a washer/nut. This served its purpose for permanent fastener installations that demanded diameters larger than conventional swaged-collar lock-bolts that were size-limited to ~0.375. In the 1950s and early 1960s fastener designers went on a weight savings binge.

This style bolt emerged: could be installed ILO the deep-head, longer-thread bolt with a lightweight nut. Shorter threads + shallow nut = lighter weight installation!
Then someone said ‘why does the head have to be that big for shear application?’... so the next evolution promoted heads ~60% depth of these bolts. The initial concern was the bolts’ head ability to absorb torque… until it was recognized that only low-height light weight shear nuts [W/WO washer] should be installed… which needed lower installation torques, so that the head recess size could shrink proportional to head size. Shallow head + short threads = even lighter weight installation

Then Hi-Shear had an inspirational break-thru! The Hi-Lok pin-collar lock-bolt system: Permanent fastener installation similar to the Bolt-Nut combination… with huge range of threaded pin/collar diameters available… blowing-away the ~3/8”diameter limitations of the swaged-collar lock-bolt design. Also, since the head drive recess went away, the tension-head, or shear-head depths could be slightly reduced: stress concentration of the drive recess [be it +, offset-+ or coin-slot, etc] is high and affects head design/stresses. Also, the patented hex-drive recess in the threaded tail of the fastener allowed the part to be torqued without the Pin spinning-around and made a little hollow-cavity in the thread-tip where stresses are low. Also the ingenious collar system allowed a stub threaded self-locking collar to remain-in-place after the driving-hex torqued it to the required limit… then broke-way! For shear-rated fasteners an aluminum collar was more than adequate; for tension-rated fasteners a similar design steel collar provided a huge increase in tensile capability. Reduced head depth + hollow-tip recess + light weight collar = a substantial weight savings over bolt/nut installations.


Then came an evolution in metallurgy: Steel HT went from 14-KSI to 160-KSI to 180+-KSI… and other alloy emerged such as Titanium, A-286 CRES etc. Bolt strength, heat resistance and strength/weight abilities skyrocketed.
Bolts, nuts, washers, Pins, collars, etc were available in a huge variety of ‘flavors’… other than the vanilla steel and aluminum in-use for decades. VHS steel alloys, Ti-6Al-4V, A286, 17-4PH, I-718, etc for Bolts/Pins [HL or swaged-collar lock-bolt, etc]… and VHS steel alloys, 303-CRES, PH-CRES, Titanium, etc for nuts, collars, washers, etc.

Immediate weight/strength gains occurred when titanium bolts are assembled with light-weight titanium or CRES nuts and washers/collars [Ti alloys are ~66% mass of steel] or aluminum collars [~0.33% mass of steel]. Just imagine how much lighter/stronger older structural aircraft designs would be if modern fasteners could be incorporated!!!… and this is exactly why new vehicle designs rarely use old design fasteners for any reason.

In this brief summary, I have only brought-you up to the early 1990s. Since then refinements to bolts/nuts have included changes to head and drive styles [6-point to 12-point, reduced drive diameters, ring-flange changes, etc] and overall strength/durability improvements due to alloy/temper/manufacturing changes [EX: strength increases from 160-to-180-KSI for titanium bolts, etc]. Changes to threaded pin-collar designs have been even more impressive: lighter pin and collar designs [shave metal here-there, tighten installation parameters, change locking mechanisms, alloy improvements, etc]; and changes to pins for better/smoother fit when installed in light-to-high interference [for improved fatigue protection, etc]… PLUS the changes mentioned above for collars, incorporated into the Pins!

Rut-Ro... Gotta go back to work.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[monkeydog]

One thing I don't understand, is if the supplier (company owner) does not have the specification, what is he fabricating the screw to?

 

[tbuelna]

wktaylor- great post as always.

Below are the titles from four NAS 100deg flush head bolt specs that illustrate your point about the slight differences for specific applications. I would add that shear bolts typically have a "close tolerance" body (shank) diameter and careful control of the thread length runout. The number of incomplete thread pitches on a shear bolt is usually held to 1 or less, while a tension bolt might allow up to 2 incomplete thread pitches. Besides the weight reduction considerations you noted, tightly controlling the thread/grip length of shear bolts makes it easier to get a consistent bearing area in the joint as well as eliminating the possibility of having the screw threads loaded in shear.

The best features of Hi-Loks are being able to torque them from one side and consistency of the fastener preload after installation. I recall being at Boeing 20 years ago doing structures work on the 737NG programs. Ti shear pins with aluminum collars were very common, and due to the large number of them used on the airframe they provided a very substantial weight reduction. Ti threaded fasteners work well for permanent attachments if they are installed under carefully controlled conditions. But Ti threaded fasteners have proven to be problematic for applications that require periodic removal/re-installation in service. Better to use cres fasteners for these situations.