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Official AN bolt material and strength specification

Official AN bolt material and strength specification

Hi, I´m a mechanical engineer with some knowledge in airplane design. I have a pilots license and have been involved in some airplane design on an EAA-basis.

 I am now designing a light biplane two-seater and I´m currently collecting all the necessary material strength data.
 My main question is: Where do I find official and up to date AN/MS specifikations for all the ordinary hardware that you need to design a light airplane.

 I don´t want to specify strength values that I found in various books or catalogues,though generally I have no reason to doubt them. I will NOT use data found directly at Internet sites.

I just want to be official because my design will be checked by the Swedish equivalent to the FAA.

 One thing I find especially irritating is that I just can´t find any official specifikation on the material of ordinary AN-bolts (AN3 to AN 20).It´s rather important since I´m going to use a lot of these bolts.

I have the latest Mil-hdbk (5J) and a wealth of information on materials from a number of sources (Books, aircraft material trading companies etc).They all tell me that AN-bolts are  made of 4037 or 8740 steel heat treated to 125 ksi tension and 75ksi shear. Mil-hdbk has data on 8740/4140 and Chapter 8, tables 8.1.5.a/b has information on strengt data for threaded fasteners heat treated to 125ksi tension and 75 ksi shear. Bruhn and the old ANC-5 has also strength data on AN-bolts (bending and combined strengths). Of course I trust Bruhn and ANC-5 (more or less) but that is strictly not official strength data.
I have a specifikation sheet on AN-bolts but it says nothing about the material, it just specifies the dimensions and tolerances. I don´t know if the "procurement specifikation" (Mil-B-6817  I think) says anything about the material because I can´t find that spec either.

Can anyone help me with this.I have no reason to doubt all the strength information I have gathered from different sources but I just want to get the official data. I found a specifikation on AN 655 (turnbuckles) but thats all.AC- 4313 has all the info on steel wires and their specifikations and I´m happy about that.

To me these are especially important questions but a lot of people just don´t seem to care very much.

Would be nice to read some comments  

RE: Official AN bolt material and strength specification

The actual AN Mil Spec ("BOLT - MACHINE, AIRCRAFT", AN3 THRU AN20 14 JAN 91) has a table of strengths. (AN is actually now obsolete, and is superseded by NASM which has the same table.) The NASM is published by the AIA:

Aerospace Industries Association of America, Inc.,
1250 Eye Street, N.W.
Washington, D.C. 20005.

For aerospace standards this website shunts you off to

where you can buy NASM3-20 and all the other NAS, etc., standards for $34 a pop.

It's similar for the MIL-B-6812 (superseded by NASM6812).

My company has a deal with IHS so that we access all the common standards online. It used to be you subscribed and got hardcopy, then that was superseded by CD-ROM, now it's via the web. It has never been cheap. How small outfits get affordable access I don't know (especially a one-man-band like yourself, be2).

It seems odd that you've got some sort of spec with the bolt dimensions but not the strength table. In the AN spec. the strengths are listed on the last page, page 4.

RE: Official AN bolt material and strength specification

I agree with rb1957, use the Assist website, download the specs (pg 4 of 4 has a strengh table), and use the table listed on the spec. Even though the P/N is SS by the NASM, there are plenty on the market that were made under the old AN p/n.

Wes C.

RE: Official AN bolt material and strength specification

Well I'll be, the assist site has the old AN standards for free. Handy.

RE: Official AN bolt material and strength specification

RP.. that Assist Site is amazing...

this will be my one and only THANK GOD FOR THE GOVT.

Wes C.

RE: Official AN bolt material and strength specification

Thanks a lot all of You, I think I can live with the old standards, I already printed and saved most of what I need them. Its amazing what good advice there is, if one only asks for it.

RE: Official AN bolt material and strength specification


1.  Sounds like You need a Boeing, Lockheed, Cessna, etc… liaison handbook, and/or design manual(s)… which have all the info You are looking for… and MUCH MORE about aero fastening. Good luck.  

2.   If this (1) is NOT feasible, then I recommend the following basic documents for starters… most easily procurable thru the web at say IHS or the FAA AC website. Some may have to be purchased at nominal cost (of doing business).

  MIL-HDBK-5 (old) or MMPDS (current) metals and fastener data and [any version].

  AN3—20 (old) or NASM3—20 (current) base spec for AN3-X to AN20-X Bolts
  Note: I recommend using newer generation hardware such as NAS6203—6220 for a number of   reasons, but most importantly higher strength, tighter tolerances and OVERSIZES are available [for “aw-sh*ts].

  AN960 or NAS1149 for washers

  AN310, AN315, AN316, AN320 [Or equiv NASMxxx], NAS679, etc Nuts

  FF-N-836 or MIL-N-25027 [NASM25027] procurement specs for Nuts

  AS567 Safetying Hardware, General Practices

  MIL-B-6812 (old) or NASM6812 (current) procurement spec for AN bolts.

  NAS618 standard fastener dimensions and hole tolerances

  MIL-STD-403C Rivet and Screw [and low-grade bolt] Installation spec

  AC43.13 for acceptable maintenance and repair techniques. [FAA website]

  ACs for general maintenance practices [specifically need procedures for Nut/Bolt Installation]

3.  How does this all work to insure a fully analyzed Bolted joint Installation??? As follows..

3.1  MIL-HDBK-5 Para 8.1.5 discusses how to analyze for “standard bolts” [not shear head, because reduced fasteners may fail the head in pin bending when shear-loaded... think-about-it].

3.2  MIL-HDBK-5 Table  8.1.5(a) defines absolute shear strength of generic “bolts”, based on known [heat treat] shear-stress capability. ANXX bolts are roughly 75-KSI and NAS62XX Bolts are 95-KSI [approx values ONLY]. NOTE: the NASM3—20 spec actually provides max rated strength for each bolt size. Example form this table for a 0.250-In diameter 75-KSI shear bolt:

P (shear-ult) = 3680-lbs

3.3  MIL-HDBK-5 Table Unit Bearing Strength of Sheet and Plate in Joints With Threaded Fasteners or Pins; Fbru = 100 KSI.  This defines bearing-tear-out for “generic 100-KSI material [try finding it]. The intent is to match fastener [hole] diameter and sheet thickness to determine a “shear ultimate”… based on 100-KSI material. This number is then factored up/down based on the FBru of the “real-world” alloy being analyzed. Example [MIL-HDBK-5J, Table]:

0.250-In Dia Hole thru 0.10-thick material (at 100-KSI Fbru) = 2500-lbs bearing force.

For 7075-T6 sheet, 0.10-thick, 2-D edge distance, from table, Fbru (A) = 156-KSI.

Therefore max allowable bearing load for this sheet metal is 156/100 x 2500-lbs = 1.56 x 2500 = 3900-lbs

3.3    Comparing shear ultimate VS material Bearing ultimate determines MAX allowed P (shear) at this location. Example [for the 0.250-dia bolt in 0.100-thick sheet]:

Bolt Shear Ult = 3680-lbs

Hole Bearing Ult = 3900-lbs

Therefore, Ult allowable load at this hole is the lesser of these loads = 3680-lbs [bolt fails slightly before the hole fully-tears-out, not a bad joint if I do say-so].

Note: this analysis presumes a "standard head bolt" with a shear-rated nut [W/WO a washer].

Regards, Wil Taylor

RE: Official AN bolt material and strength specification

Hi,Wil, thanks for Your comments.

I have the Mil-hdk 5-J, AC 43-13 and a number of fairly up to date hardware specifikations that I recently downloaded . It´s very nice that someone takes the inconvenience to diskuss the analyze of a bolt fitting.

 I work as a consultant mechanical design engineer, doing various small CAD-engineered projekts in that field (currently designing a horrible smelling food-waste pump for restaurants). So I´m supposed to do stress calculations now and then, but it seldom happens. I am very interested though in airplane stress calculations and think I have a fairly good idea what it´s all about. That´s why I´m a stickler about specifikations and getting the numbers right.

 In my little private project I try to run it as a professional would do, from two reasons: In the long run it will help me to get my design cleared without discussions (and redesign) and I myself will feel a lot more confident at the time of getting the thing off the ground.

 About bolted joints: I have a lot of information from Bruhn etc (lug analysis, multiple bolt joints etc) and I think it makes sense to try to analyze my fittings using various assumptions. I will also separately stress test all fittings that I´m unsure of,and that´s a good practice when it comes to FEA analyzed fittings too, besides testing the whole airplane.

So, thanks Wil, for running the example from the Mil-hdbk, it´s very reassuring for me that I understand what You´re talking about since I don´t have contacts with any real knowledge in airplane design, that I can share my ideas with.
 I don´t know if it´s necesarry to use high strength bolts except in a few areas. Many of my fittings will be bolted to wooden mebers (I have a copy of ANC-18 and -19) and I guess its wooden bearing strength that is often critical there. The reasons You give for using higher strength (and oversize) bolts are however very well worth of considering. I hadn´t thought of the {aw-sh*ts}until now.

As for sheet material it will be mainly 4130N since I think it will be the easiest and cheapest to find. I don´t think I will try to trade sheet thickness for high strength (buckling considerations) except maybe if I really gain something with it.


RE: Official AN bolt material and strength specification


4130N maybe be cheap, but the resulting design will be heavy.  i would have thought that if you could get 4130N, then you could get 4130 "1/4hard" (125ksi).  possibly buy the annealled condition, then heat treat (possibly after forming) ... shouldn't distort too much

good luck with your project

RE: Official AN bolt material and strength specification

Thanks, I need all he luck I can get.I try to keep it as simple and cheap as possible, and I will keep radiuses gentle and large so I won´t have to stress releive the fitings.

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