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NAS1351 Minimum Strength Note Question

NAS1351 Minimum Strength Note Question

NAS1351 Minimum Strength Note Question

(OP)
Hello, the spec for this fastener lists "Minimum Breaking Strength" in pounds and has a note saying: "MINIMUM BREAKING STRENGTH VALUES ARE BASED ON 180 KSI HEAT TREATMENT. LINED THROUGH STRENGTH VALUES WERE BASED ON 170 KSI"

Perhaps I am not familiar with the term, but what does 'lined through strength' refer to? Any info would be great.

RE: NAS1351 Minimum Strength Note Question

The answer spans spec NAS1351 and the procurement spec FF-S-86...

1. NAS1351...

Table II Minimum Breaking Strength (LBF)
'Alloy steel' [column]
Diameters -4, -5, -6, -7, -8 [-8 = 1/2"-Dia]

6,200 6,550 /h/
9,850 10,400 /h/
14,900 15,800 /h/
20,200 21,400 /h/
27,000 28,800 /h/

/h/ MINIMUM BREAKING STRENGTH VALUES ARE BASED ON 180 KSI HEAT TREATMENT. LINED THROUGH STRENGTH VALUES WERE BASED ON 170 KSI.


2. Per the procurement specification FF-S-86...

3.2 Mechanical properties.
3.2.1 Alloy steel cylindrical head cap screws. Ultimate tensile strength
and hardness of alloy steel cylindrical head cap screws shall conform to the
following:
(a) Ultimate tensile strength
(1) Sizes .060 through .500 inch •••••••••••••• 180,000 PSI min
(2) Sizes over .500 inch •••••••••••••••••• l70,000 PSI min


3. Summary/Conclusions...

3.1 IF the NAS1351 are to-be made/qualified per FF-S-86, then it is mandatory for screws made from alloy steel to 'meet' ultimate tensile [breaking] strength per FF-S-86 Table II.

3.2 For all NAS1351 screws 0.500-Dia, and smaller Dia, it is mandatory for them to attain UTS of 180-KSI

3.3 For all NAS1351 screws larger-than 0.500-Dia, it is mandatory for them to attain UTS of 170-KSI

3.4 Obviously for screws 0.500-Dia and smaller there was a 'awsh*t', when spec was introduced... and these smaller Diameters only required [in the NAS1351 spec] to meet UTS of 170-KSI... which did NOT conform with long-standing MANDATORY requirements of FF-S-86 to meet UTS of 180-KSI.

3.5 AIA/NAS elected to leave the UTS 170-KSI values on Table II as 'a record of the prior requirement'... but 'struck-thru these values' making them no longer valid/applicable... and added the appropriate [UTS 180-KSI] values that current production fasteners MUST attain.

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]

RE: NAS1351 Minimum Strength Note Question

(OP)
Thank you Wil! This makes sense. It didn't occur to me that 'lined through' referred to the crossed out data. Your insight is much appreciated!

RE: NAS1351 Minimum Strength Note Question

Something similar happened [or should happen] with Titanium bolts...

1. Hex Bolts... example...

Procurement spec NAS4004 does NOT include diameters greater than 0.7500 [Nom/X/Y], so sizes 14, 16, 18 and 20 were 'lined-out' with flag note explanation.

NAS6403-to-6420 hex head bolts, short thread, Ti, nom/X/Y Dia

NAS6803-to-6820 hex head bolts, short thread, Ti, nom/X/Y Dia

2. Flush head Bolts... odd contradiction... Dias NOT lined-out when they should be lined-out... example...

Procurement spec NAS4004 does NOT include diameters greater than 0.7500 [Nom/X/Y]... but, interestingly/oddly, sizes 14 and 16 have NOT been 'lined-out' [as of latest spec revisions that I have] in these specs...

I doubt if the 14 or 16 Dias would even be available, due to spec contradictions...

NAS7303-to-7316 FT head bolts, long thread, Ti, nom/X/Y Dia

NAS7603-to-7616 FT head bolts, short thread, Ti, nom/X/Y Dia

NAS8802-to-8816 FS head bolts, short thread, Ti, nom/X/Y Dia

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]

RE: NAS1351 Minimum Strength Note Question

(OP)
Thank you again! Great info.

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