Metric Aircraft Hardware

[old man emu]

Please pardon this post, which some may see as advertising, but it's not meant to be.

 

I was wondering if LSA aircraft built or sourced from Europe use Metric or Imperial nuts and bolts in their construction.

 

If so, can metric hardware be sourced in Australia.

 

Old Man Emu

 

 

[Yenn]

I can't answer your question, but I am building an RV4 and it takes me back to childhood. What a bastard of a job adding 21 13/16 for example to 2 7/8. A sure way to make a mistake. I have got the design for a fraction adding calculator but even using that is a pain. Luckily I have an electronic calculator that accepts fractions and turns them into decimals.

 

 

[bones]

I just dont get the AN measuring system at all, proves i must be dumb i guess.

 

 

[facthunter]

metric Nuts/ bolts.

 

I believe the Technam is all metric. I would expect that all European aircraft would use Metric and that American built craft would be their own which was derived from the older and now defunct, SAE. Unified threads came next. (UNF. UNC) . Aren't AN the american standard? British had BSF/ whitworth, BA for instruments, and many others. What a mess!!!. Nev

 

 

[old man emu]

I just dont get the AN measuring system at all, proves i must be dumb i guess.

It's quite easy, really.

 

The AN, NAS and MS systems are based on 1/16" and 1/8".

 

The diameter of bolts is given in 1/16". Bolts in the AN3 group have a diameter of 3/16"; AN4 = 4/16" (1/4"); AN5 = 5/16" etc.

 

The length of AN bolts is given in 1/8" increments, with the shortest length being 3/8". Therefore an AN4 bolt which is 5/8" long is an AN4-5

 

The confusing thing is that there are no -8 or -9 lengths. This is because a -8 bolt length is 8/8" long, which is 1" (written 10), and a -9 bolt would be 9/8" long or (1 + 1/8") which is writen 11. Therefore an AN3 bolt which is 8/8" long is an AN3-10, and a 1-1/8" long AN3 bolt is an AN3-11.

 

As the bolts get longer, you get up into the 20's, 30's, 40's etc. For example a bolt with a half inch diameter, 3-5/8 long is an AN8-35.

 

Then there are code letters describing the holes drilled in a bolt. A bolt described as an AN4-5 has a hole drilled through the threads to accept a split pin. The same length bolt without a hole is an AN4-5A, where A stands for "absent".

 

If there was a hole drilled in the head of the bolt, it would be an AN4H5A. With holes in the head and threads it would be an AN4H5.

 

Here endeth the First Lesson.

 

Old Man Emu

 

 

[planedriver]

I'm in the process of rebuilding an Evinrude 115hp V4 powerhead to replace the one on my boat. I stripped it all down, split the crankcase and then came to grinding halt for a suitable socket to undo the big-end bearing caps. I was told so many different things by various outboard repairers and even ordered a socket from Melbourne which turned out to be way too big. This afternoon my crook back was made to suffer a bit more, after lugging the block into the boot of the car and doing The Cooks Tour of tool shops. After more than a week of trying, I eventually found a metric 12 point socket that fitted perfectly, so felt very relieved.

 

If there was one range of standard threads with simple identifiable markings on nuts and bolts, life would be easier for so many mortals like me. But I realise that some threads are more suitable for certain applications.

 

Anyway, if you get woken up with a wroom! wroom! noise early on Sunday morning, it's possibly me:big_grin:

 

Regards

 

Alan

 

PS. It seems I should have contacted Old Man Emu for a few clues, as he seems a "knowledgeable nut" to coin a phrase.

 

 

[Guest JRMobile]

OME

 

That is one of the easiest/best description I have seen to explain the AN bolt setup :thumb_up:.

 

Thanks for sharing.

 

Cheers John

 

 

[Old Koreelah]

Thanks you, old man emu, for your Rosetta Stone of aircraft bolt sizes. At last I can make some sense of the mess. The most valid comment is the "hole in the head" -not the bolt's head- that seems to be suffered by the powers that be; we metricated decades ago, now I have difficulty finding anything described in metric, The stuck-in-the-mud Americans are holding the world back!

 

 

[Ding]

Metric aircraft / bolts

 

Back to the original question. My Skyranger was manufactured in Europe, and all the bolts in the kit were metric. All the drilled holes were metric. So worked fine.

 

Problem is that there are not the small increment sizes available in metric that there are in the AN series, so you end up with more than 2 threads showing in most cases. Sometimes it flukes it and you get just 2 clear threads showing.

 

Other problem is that sometimes you end up with a part of the load bearing on the thread because the threaded part is to long.

 

You could replace the metric bolts with AN but there is no perfect equivalent metric size for the fractional sizes, so you would have to drill all the holes to suit AN. OK if you are starting out with a blank sheet, but in my case I wasn't about to start removing metal or have bolts rattling in too big holes. Not being an engineer I didn't want to change anything from the design.

 

Having said all that, my Sky is now 3 years old, and nothing has fallen off, no bolts have broken and when inspected closely, there doesn't seem to be any chaffing where the thread is "down the hole".

 

The next part of the problem is that you can never be sure of just how well controlled the manufacturing process has been with metric bolts bought off the shelf. AN are carefully controlled so they meet a defined standard because they are used in aircraft.

 

I guess if the aircraft is designed for metric, with the above things considered, then all should be well. At some point we just need to trust the designers.

 

There was a good article/s in fairly recent RAAus magazines on just this subject. In the last 12 months by memory.

 

Thats been my experience anyway. Over to the experts.

 

Ding.

 

PS. That was the best desciption of the AN sizing process I have ever seen. Good job.

 

 

[Yenn]

The AN system is not a system of measurement. It is a system of quality control. An AN3 bolt is not a 3/16" bolt, but a bolt of 3/16" dia that conforms to certain standards of manufacture and materials. AN does not only apply to bolts, but a whole host of aircraft hardware including fuel fittings and rivets. And AN stands for Airforce Navy, having its background in the military sphere.

 

As far as finding the right spanner or socket for a bolt, just take a measurement of the distance across the flats and that will tell you what you want, except for odball heads with other than 6 or 4 sides.

 

 

[Smokey]

I believe the Technam is all metric.

I've been looking throught the Foxbat builders manual, and they are all metric.

 

So back to OME's original question, does anyone know a source for aircraft standard metric bolts, screws & fittings ?

 

I for one would be very interested to know a source other than the aircraft's agent to at least compare pricing.

 

If someone out there sells this stuff and is concerned about breaching forum advertising guidelines please feel free to PM me.

 

Mark

 

 

[Guest ozzie]

Find someone who owns or works on Trinidads or Tobagos they are metric from memory.

 

 

[Guest ozzie]

Maddog Composites

 

maybe this guy

 

 

[Bill Hamilton]

Airforce Navy,

Yenn,

Actually is (was) Army Navy, the USAF did not come into existence until after WW11. The AN standards go back pre-WW11.

 

AN standards were superseded by MS, and more recently a new universal US standard.

 

Regards,

 

PS:

 

Two threads showing is the minimum, and having any threads "down the hole" is a really bad idea.

 

I will bet a good proportion of the bolts ( with threads down the hole) are in shear, not tension, and I will further bet that the result is that the whatever fitting puts the bolt in single shear, instead of the designer intended double shear.

 

Thus doubling the shear load on the bolt x-section.

 

A great recipe for failure, and if it is something like a wing strut, drag brace etc., a failure is going to cut your future aviating very short.

 

 

[old man emu]

Actually AN, MS and NAS systems are cataloguing systems, and each type of thing has its defined specification.

 

The first system was AN, which is a USA system where the military set the specifications when it let the tenders for production.

 

The next system was the MS one, where once again the military published a specification for tenderers. In some cases the original AN descriptor was replaced by an MS descriptor, and the AN was deemed "Not Suitable for Design" after certain dates. You can still use a superceded AN part as a replacement in an aircraft designed before that date, but you can't call up a superceded AN part number when designing after that date. These dates vary from item to item.

 

Another system is the NAS system, which once again is used to replace AN descriptors.

 

If you happen to have a de Haviland, or other British built antique aricraft - good luck. You're on your own, brother.

 

Then, of course, we've got the European designed aircraft. Right now, I'm searching the world for some MS bolts for a Tecnam to replace metric ones. The manufacturer has specified some rarely used MS bolts as replacements for metric bolts in the undercarriage.

 

A WORD OF WARNING

 

If you are replacing hardware on fuel or oil hoses, take a look at the items. If they have the letters "AN" stamped on them, you can't pop into your local auto shop, or Pirtek dealer and buy fittings from them. The thread design of AN fittings is different from that of automotive fittings, and you will not get a correct seal. You may strip the thread on an expensive engine part as well.

 

Old Man Emu

 

 

[Guest ozzie]

Grab yourself a copy of the 'Standard Aircraft Handbook" there's a couple of different versions of it. If you work on your own aircraft it is a MUST have. maybe Ian has it in the shop.

 

 

[Yenn]

Not only are hydraulic threads different, the flare angle is 37 deg, not 45. I sometimes wonder if these differences are there just to make you buy more expensive equipment and tools.

 

 

[old man emu]

If someone out there sells this stuff and is concerned about breaching forum advertising guidelines please feel free to PM me. Mark

My intention in starting this thread was to get info from aircraft owners who did have aircraft with metric hardware.

 

Since I do have a thread in the Sellers folder, I was going to advertise there if I could find a source and get supplies.

 

I will definately NOT be PMing anyone to get sales. You'll have to check out that folder.

 

Old Man Emu

 

 

[Bill Hamilton]

The thread design of AN fittings is different from that of automotive fittings,

Folks,

 

If you don't require certified parts, JIC hydraulic fittings have the same form as AN/MS hose fittings.

 

The major difference between SAE (automotive) and AN/MS/JIC is the angle of the mating surfaces, being 37.5 degrees for AN etc, and 45 degrees for SAE, hence the guaranteed leaks if you mix them up.

 

Again, if you don't require certified parts, several manufacturers put out a wide range of AN etc. equivalent hose fittings for general (mostly hot rods, drag/competition cars) use.

 

There is usually a very good range of stuff, at very good prices, on US e-Bay.

 

As the previous poster says, AN/MS covers the whole range of aviation, not just hardware. For example AN 4101 covers a range of manufacturers fuel pumps, all interchangeable, and found on such as the P&W R-1830 and the Wright R-1820.

 

Regards,